The word Grace or χάρις (Charis) in Greek was in use for several hundred years before the authorship of 2nd Corinthians in both secular and Jewish writings prior to the coming of Christ and the authorship of the Epistles. As such χάρις (Charis) as it was used in 2nd Corinthians 12:9 would have been absolutely familiar to a native Greek speaker and its meaning was unchanged by the New Testament writers.
χάρις in secular usage
For example, Xenophon, a secular Greek philosopher, historian, soldier, mercenary, and a student of Socrates who lived from 431-354BC used χάρις (Charis) as a term of benevolence in his work Agesilaus which summarizes the life of King Agesilaus II in 2:29:
For he believed that at one stroke he would repay the Egyptian for his good offices to Sparta, would again set free the Greeks in Asia, and would chastise the Persian for his former hostility, and for demanding now, when he professed to be an ally of Sparta, that her claim to Messene should be given up.
ἐνόμιζε γὰρ τῇ αὐτῇ ὁρμῇ τῷ μὲν Αἰγυπτίῳ χάριν ἀποδώσειν ἀνθ᾽ ὧν εὐεργετήκει τὴν Λακεδαίμονα, τοὺς δ᾽ ἐν τῇ Ἀσίᾳ Ἕλληνας πάλιν ἐλευθερώσειν, τῷ δὲ Πέρσῃ δίκην ἐπιθήσειν καὶ τῶν πρόσθεν καὶ ὅτι νῦν σύμμαχος εἶναι φάσκων ἐπέταττε Μεσσήνην ἀφιέναι.
Similarly, in Anabasis book 3 Chapter 3 verse 14, Xenophon uses this as a term of thanksgiving for divine grace
Let us thank the gods, therefore, that they came, not with a large force, but with a handful, so that without doing us any great damage they have revealed our needs.
τοῖς οὖν θεοῖς χάρις ὅτι οὐ σὺν πολλῇ ῥώμῃ ἀλλὰ σὺν ὀλίγοις ἦλθον, ὥστε βλάψαι μὲν μὴ μεγάλα, δηλῶσαι δὲ ὧν δεόμεθα.
And also in Book 2 Chapter 5 Verse 14::
Again, take those who dwell around you: if you chose to be a friend to any, you could be the greatest possible friend, while if any were to annoy you, you could play the part of master over them in case you had us for supporters, for we should serve you, not merely for the sake of pay, but also out of the gratitude that we should feel, and rightly feel, toward you, the man who had saved us.
ἀλλὰ μὴν ἔν γε τοῖς πέριξ οἰκοῦσι σὺ εἰ μὲν βούλοιο φίλος ὡς μέγιστος ἂν εἴης, εἰ δέ τίς σε λυποίη, ὡς δεσπότης ἂν ἀναστρέφοιο ἔχων ἡμᾶς ὑπηρέτας, οἵ σοι οὐκ ἂν μισθοῦ ἕνεκα ὑπηρετοῖμεν ἀλλὰ καὶ τῆς χάριτος ἣν σωθέντες ὑπὸ σοῦ σοὶ ἂν ἔχοιμεν δικαίως.
He also goes on to use the term in several other writings including Cyropaedia, Hellenica, Memorabilia, Hiero, Oeconomicus.
In fact, it is used not just by Xenophon, but numerous other secular Greek authors including Aeschines (389-314 BC), Aeschylus (523-426 BC), Andocides (440-390 BC), Antiphon (480-411 BC), Aristophanes (446-386 BC), Demosthenes (384-322 BC), Euripides (480-406 BC), Isocrates (436-338 BC), Lycurgus (390-324 BC), Pausanias (Circa 420 BC) Thucydides (460-400 BC), Sophocles (497-406 BC), Hesiod (Circa 750-650 BC) and Homer (Circa 650-200BC)
For example the historian Polybius (200-118 BC) uses it in Book 2, Chapter 22 Verse 5 of his Histories
possessing themselves of all it contained, and, after remaining masters of the city for seven months, had finally given it up of their own free will and as an act of grace, and had returned home with their spoil, unbroken and unscathed.
γενόμενοι δὲ καὶ τῶν ὑπαρχόντων ἁπάντων ἐγκρατεῖς καὶ τῆς πόλεως αὐτῆς ἑπτὰ μῆνας κυριεύσαντες, τέλος ἐθελοντὶ καὶ μετὰ χάριτος παραδόντες τὴν πόλιν, ἄθραυστοι καὶ ἀσινεῖς ἔχοντες τὴν ὠφέλειαν εἰς τὴν οἰκείαν ἐπανῆλθον.
This term also appears in The Philosopher Plato's (428-327BC) Republic Book I Secion 338a
Nay, it is more reasonable that you should be the speaker. For you do affirm that you know and are able to tell. Don't be obstinate, but do me the favor to reply and don't be chary1 of your wisdom, and instruct Glaucon here and the rest of us.
<εἰκὸς λέγειν: σὺ γὰρ δὴ φῂς εἰδέναι καὶ ἔχειν εἰπεῖν. μὴ οὖν ἄλλως ποίει, ἀλλὰ ἐμοί τε χαρίζου ἀποκρινόμενος καὶ μὴ φθονήσῃς καὶ Γλαύκωνα τόνδε διδάξαι καὶ τοὺς ἄλλους.
And he also uses the term in his works Laws, Apology, Euthyphro, Phaedo, Theaetetus, Phaedrus, Laches, Gorgias, Lesser, Hippias and Menexenus.
The Greek historian Herodotus who lived from 484 BC to 425 BC used it several times:
Herodotus Book 3: Thaleia 
"O most noble of men, thou art he who when as yet I had no power gavest me a gift, small it may be, but nevertheless the kindness is counted with me to be as great as if I should now receive some great thing from some one."
ὦ γενναιότατε ἀνδρῶν, σὺ κεῖνος εἶς ὃς ἐμοὶ οὐδεμίαν ἔχοντί κω δύναμιν ἔδωκας εἰ καὶ σμικρά, ἀλλ᾽ ὦν ἴση γε ἡ χάρις ὁμοίως ὡς εἰ νῦν κοθέν τι μέγα λάβοιμι· ἀντ᾽ ὧν τοι χρυσὸν καὶ ἄργυρον ἄπλετον δίδωμι, ὡς μή κοτέ τοι μεταμελήσῃ Δαρεῖον τὸν Ὑστάσπεος εὖ ποιήσαντι.
Herodotus Book 8: Urania 
We admire however the forethought which ye had with regard to us, in that ye took thought for us who have had our substance destroyed, and are willing to support the members of our households; and so far as ye are concerned, the kindness has been fully performed: but we shall continue to endure as we may, and not be a trouble in any way to you.
καὶ ὑμῖν μὲν ἡ χάρις ἐκπεπλήρωται, ἡμεῖς μέντοι λιπαρήσομεν οὕτω ὅκως ἂν ἔχωμεν, οὐδὲν λυπέοντες ὑμέας. νῦν δέ, ὡς οὕτω ἐχόντων, στρατιὴν ὡς τάχιστα ἐκπέμπετε
Herodotus Book 3: Thaleia 
Thou didst exceedingly well, and double thanks are due to thee, for thy words and also for thy gift; and we invite thee to come to dinner.
κάρτα τε εὖ ἐποίησας καὶ χάρις διπλῆ τῶν τε λόγων καὶ τοῦ δώρου, καί σε ἐπὶ δεῖπνον καλέομεν.
Herodotus Book 5: Terpsichore 
While however they were preparing to take vengeance, a matter arose from the Lacedemonians which provided a hindrance to them: for the Lacedemonians, having learnt that which had been contrived by the Alcmaionidai with respect to the Pythian prophetess, and that which had been contrived by the Pythian prophetess against themselves and the sons of Peisistratos, were doubly grieved, not only because they had driven out into exile men who were their guest-friends, but also because after they had done this no gratitude was shown to them by the Athenians.
ἐς τιμωρίην δὲ παρασκευαζομένοισι αὐτοῖσι ἐκ Λακεδαιμονίων πρῆγμα ἐγειρόμενον ἐμπόδιον ἐγένετο. πυθόμενοι γὰρ Λακεδαιμόνιοι τὰ ἐκ τῶν Ἀλκμεωνιδέων ἐς τὴν Πυθίην μεμηχανημένα καὶ τὰ ἐκ τῆς Πυθίης ἐπὶ σφέας τε καὶ τοὺς Πεισιστρατίδας συμφορὴν ἐποιεῦντο διπλῆν, ὅτι τε ἄνδρας ξείνους σφίσι ἐόντας ἐξεληλάκεσαν ἐκ τῆς ἐκείνων, καὶ ὅτι ταῦτα ποιήσασι χάρις οὐδεμία ἐφαίνετο πρὸς Ἀθηναίων
And geographer, philosopher and historian Strabo (64 BC - 24 AD) uses the term in Geographica, Book 9, Chapter 2, Verse 40
And of its power there is this proof, that the Thebans were wont to pay tribute to the Orchomenians and to Erginus their tyrant, who is said to have been put to death by Heracles. Eteocles, one of those who reigned as king at Orchomenus, who founded a temple of the Graces, was the first to display both wealth and power; for he honored these goddesses either because he was successful in receiving graces, or in giving them, or both.
τῆς δυνάμεως δέ, ὅτι Θηβαῖοι δασμὸν ἐτέλουν τοῖς Ὀρχομενίοις καὶ Ἐργίνῳ τῷ τυραννοῦντι αὐτῶν, ὃν ὑφ᾽ Ἡρακλέους καταλυθῆναί φασιν. Ἐτεοκλῆς δέ, τῶν βασιλευσάντων ἐν Ὀρχομενῷ τις, Χαρίτων ἱερὸν ἱδρυσάμενος πρῶτος ἀμφότερα ἐμφαίνει, καὶ πλοῦτον καὶ δύναμιν, ὃς εἴτ᾽ ἐν τῷ λαμβάνειν χάριτας εἴτ᾽ ἐν τῷ διδόναι κατορθῶν εἴτε καὶ ἀμφότερα, τὰς θεὰς ἐτίμησε ταύτας.
Finally, Dionysius of Halicarnassus (60-7 BC), uses the word in his work De Compositione Verborum (pg 241):
Here the euphonious effect and the grace of the language arise from the coherence and smoothness of the junctures.
ταύτης τῆς λέξεως ἡ εὐέπεια καὶ ἡ χάρις ἐν τῇ συνεχείᾳ καὶ λειότητι γέγονε τῶν ἁρμονιῶν: παράκειται γὰρ ἀλλήλοις τὰ ὀνόματα καὶ συνύφανται κατά τινας οἰκειότητας καὶ συζυγίας φυσικὰς τῶν γραμμάτων:
From the above examples, you can see that χάρις (Charis) had a range of meanings which included χάρις (Charis) as an act of benevolence, χάρις (Charis) as a quality or character trait (which can also be seen through the usage of the root χάρις [Charis] in the word
greek word χαρισμα [Charisma]), and finally the concept of giving χάρις (Charis) which is to give worship or thanksgiving to one's benefactor. In fact, usage of χάρις (Charis) and its' congugates are recorded over 200 times in secular works with the majority of uses appearing before Pauline writings.
χάρις in Septuagintal usage
The Septuagint is a Greek translation of the Old Testament (Torah) from Hebrew. This is an extremely useful tool for comparing and contrasting how meaning is is understood once translated by the Greek audience of Jesus time, modern English readers and the origional Hebrew audience. For example, you can begin to see doctrines arise based on the Greek translations of the Torah.
In our case however, these writings also would have an irrevocable impact on the secular understanding of χάρις (Charis) since the Septuagint predates the birth of Christ by a couple hundred years and the Septuagint can serve to demonstrate that there was no difference between secular usage and religious meaning prior both to the birth of Christ and the penning of the Pauline Epistles. A more useful question is not if Paul imbued χάρις (Charis) with new meaning, but instead if the translators of the Septuagint imbued new meaning hundreds of years earlier (to which the answer is still "no" based on the above examples)
From Apocraphal Texts
This can firstly be seen in Apocraphal or non-canonical works
Wisdom of Solomon 3:9
They that put their trust in him shall understand the truth: and such as be faithful in love shall abide with him: for grace and mercy is to his saints, and he hath care for his elect.
οἱ πεποιθότες ἐπ᾿ αὐτῷ συνήσουσιν ἀλήθειαν, καὶ οἱ πιστοὶ ἐν ἀγάπῃ προσμενοῦσιν αὐτῷ, ὅτι χάρις καὶ ἔλεος ἐν τοῖς ὁσίοις αὐτοῦ, καὶ ἐπισκοπὴ ἐν τοῖς ἐκλεκτοῖς αὐτοῦ.
Wisdom of Solomon 4:15
This the people saw, and understood it not, neither laid they up this in their minds, That his grace and mercy is with his saints, and that he hath respect unto his chosen.
ὅτι χάρις καὶ ἔλεος ἐν τοῖς ἐκλεκτοῖς αὐτοῦ καὶ ἐπισκοπὴ ἐν τοῖς ὁσίοις αὐτοῦ.
Wisdom of Sirach 4:21
For there is a shame that bringeth sin; and there is a shame which is glory and grace.
ἔστι γὰρ αἰσχύνη ἐπάγουσα ἁμαρτίαν, καὶ ἔστιν αἰσχύνη δόξα καὶ χάρις.
Wisdom of Sirach 20:13, 16
A wise man by his words maketh him beloved: but the graces of fools shall be poured out.
ὁ σοφὸς ἐν λόγῳ ἑαυτὸν προσφιλῆ ποιήσει, χάριτες δὲ μωρῶν ἐκχυθήσονται.
The fool saith, I have no friends, I have no thank for all my good deeds, and they that eat my bread speak evil of me.
μωρὸς ἐρεῖ· οὐχ ὑπάρχει μοι φίλος, καὶ οὐκ ἔστι χάρις τοῖς ἀγαθοῖς μου· οἱ ἔσθοντες τὸν ἄρτον μου, φαῦλοι γλώσσῃ·
Wisdom of Sirach 26:13-15
The grace of a wife delighteth her husband, and her discretion will fatten his bones.
χάρις γυναικὸς τέρψει τὸν ἄνδρα αὐτῆς, καὶ τὰ ὀστᾶ αὐτοῦ πιανεῖ ἡ ἐπιστήμη αὐτῆς. δόσις Κυρίου γυνὴ σιγηρά, καὶ οὐκ ἔστιν ἀντάλλαγμα πεπαιδευμένης ψυχῆς.
Wisdom of Sirach 32:10
Before the thunder goeth lightning; and before a shamefaced man shall go favour.
πρὸ βροντῆς κατασπεύδει ἀστραπή, καὶ πρὸ αἰσχυντηροῦ προελεύσεται χάρις.
Wisdom of Sirach 37:5, 11, 21
There is a companion, which helpeth his friend for the belly, and taketh up the buckler against the enemy.
ἑταῖρος φίλῳ συμπονεῖ χάριν γαστρός, ἔναντι πολέμου λήψεται ἀσπίδα.
Neither consult with a woman touching her of whom she is jealous; neither with a coward in matters of war; nor with a merchant concerning exchange; nor with a buyer of selling; nor with an envious man of thankfulness; nor with an unmerciful man touching kindness; nor with the slothful for any work; nor with an hireling for a year of finishing work; nor with an idle servant of much business: hearken not unto these in any matter of counsel.
μετὰ γυναικὸς περὶ τῆς ἀντιζήλου αὐτῆς καὶ μετὰ δειλοῦ περὶ πολέμου, μετὰ ἐμπόρου περὶ μεταβολίας καὶ μετὰ ἀγοράζοντος περὶ πράσεως, μετὰ βασκάνου περὶ εὐχαριστίας καὶ μετὰ ἀνελεήμονος περὶ χρηστοηθείας, μετὰ ὀκνηροῦ περὶ παντὸς ἔργου καὶ μετὰ μισθίου ἐφεστίου περὶ συντελείας, οἰκέτῃ ἀργῷ περὶ πολλῆς ἐργασίας, μὴ ἔπεχε ἐπὶ τούτοις περὶ πάσης συμβουλίας·
For grace is not given, him from the Lord, because he is deprived of all wisdom.
οὐ γὰρ ἐδόθη αὐτῷ παρὰ Κυρίου χάρις, ὅτι πάσης σοφίας ἐστερήθη.
From the Old Testament
And secondly, from the Old Testament
Proverbs 22:1 (Click here for English versions in Parallel)
A fair name is better than much wealth, and good favour is above silver and gold.
ΑΙΡΕΤΩΤΕΡΟΝ ὄνομα καλὸν ἢ πλοῦτος πολύς, ὑπὲρ δὲ ἀργύριον καὶ χρυσίον χάρις ἀγαθή,
Ecclesiastes 9:11 (Click here for English versions in Parallel)
I returned, and saw under the sun, that the race is not to the swift, nor the battle to the strong, nor yet bread to the wise, nor yet wealth to men of understanding, nor yet favour to men of knowledge; for time and chance will happen to them all.
᾿Επέστρεψα καὶ εἶδον ὑπὸ τὸν ἥλιον ὅτι οὐ τοῖς κούφοις ὁ δρόμος καὶ οὐ τοῖς δυνατοῖς ὁ πόλεμος καί γε οὐ τῷ σοφῷ ἄρτος καί γε οὐ τοῖς συνετοῖς πλοῦτος καί γε οὐ τοῖς γινώσκουσι χάρις, ὅτι καιρὸς καὶ ἀπάντημα συναντήσεται τοῖς πᾶσιν αὐτοῖς.
Ecclesiastes 10:12 (Click here for English versions in Parallel)
The words of a wise man’s mouth win him favor, but the lips of a fool consume him.
λόγοι στόματος σοφοῦ χάρις καὶ χείλη ἄφρονος καταποντιοῦσιν αὐτόν
Psalms 45:2 (Click here for English versions in Parallel)
You are fairer than the sons of men; Grace is poured upon Your lips; Therefore God has blessed You forever.
ὡραῖος κάλλει παρὰ τοὺς υἱοὺς τῶν ἀνθρώπων, ἐξεχύθη χάρις ἐν χείλεσί σου· διὰ τοῦτο εὐλόγησέ σε ὁ Θεὸς εἰς τὸν αἰῶνα
Based on all of the above cited instances (and more) the Lexicons rightly1 2 show that the semantic meaning and range of χάρις (Charis) is:
(1) a wining quality or attractiveness that invites a favorable reaction
(2) a beneficient disposition towards someone
(a) A generosity granted to another
(b) A generosity that one experiences
(3) the practical application of goodwill
(a) by men
(b) by a divine deity
(4) an exceptional effect produced by generosity (favor)
(5) response to generosity or beneficience
The Greek-English Lexicon of the New Testament and Other Early Christian Literature 1 also notes that
It seems that χάρις is not always clearly differentiated in meaning From χαρά (Joy). For example, in the Second Century BC
Apollodorus used the word in this way: 244 Fgm. 90 Jac. says in the second book περὶ θεῶν: κληθῆναι δὲ αὐτὰς ἀπὸ μὲν τ. χαρᾶς Χάριτας· καὶ γὰρ πολλάκις … οἱ ποιηταὶ τ. χάριν χαρὰν καλοῦσιν ‘the [deities] Charites are so called from χαρά [joy], for poets freq. equate χάρις with χαρά’. Cp. the wordplay AcPl Ha 8, 7 χαρᾶς καὶ χάριτος the house was filled with gaiety and gratitude.).
What is more interesting (to this author at least) is not if any meaning was added by more modern writings and translations, but instead what meaning has been lost. While we may have an idea of thanksgiving or gratitude in modern Western society, this activity stops at a feeling. Instead, the idea of "giving grace" as an act of thanksgiving is lost to modern audiences. Instead of being required to "pay it forward" by giving to others the same radical benevolence we outselves have received, we must merely "give thanks". While "giving grace: historically would have been seen as an indicator that Israelite should make sacrifices at the temple, Jesus radically alters the meaning of this edict in Luke 6:36), saying
Be merciful, just as your Father is merciful.
we only need be "thankful" for what we have received.
In contrast, the idea of "giving grace" requires that we live an inaugurated eschatology in which Christ is (in some small part) incarnate in each of us and made manifest in the world around us through our acts of grace.
In short, χάρις (Charis) as it was used in 2nd Corinthians 12:9 would have been absolutely familiar to a native Greek speaker and the meaning of χάρις (Charis) was left unaltered by the New Testament writers.
1 Arndt, William ; Danker, Frederick W. ; Bauer, Walter: A Greek-English Lexicon of the New Testament and Other Early Christian Literature. 3rd ed. Chicago : University of Chicago Press, 2000, S. 1079
2 While the above list is based on the BDAG1 A Greek-English Lexicon by Henry George Liddell and Robert Scott (the LSJ) records similar application and meaning.