In Genesis 23, we learn that Sarah has died and Abraham is looking to acquire a grave for her. He approaches the children of Heth and meets Ephron the Hittite who, initially, offers his land (which includes the Cave of Machpellah) for free, giving the appearance that he is very generous. At this point his name (Gen. 23:10-11), in the Hebrew text, is spelled Ayin-Feh-Resh-Vav-Nun. At verse 14, Ephron names his price, "My lord, hearken unto me: a piece of land worth four hundred silver shekels, what is that between me and you? Bury your dead. J.H. Hertz tells us that Ephron has just suggested an exorbitant amount which, according to the Code of Hammurabi, the annual wages of a working man during that era would be six to eight regular shekels. At verse 16, Abraham pays the price, and the Bible removes the vav from Ephron's name (as if I spelled it "Ephrn" -- you'd be able to pronounce it, but you would assume the letter "o") after he accepts the money. Is that spelling change intentional? If so, what message is being sent?
The classic Jewish commentator Rashi quoting the Medrash and the Talmud says:
and Abraham weighed out to Ephron: עֶפְרֹן is spelled without a “vav,” because he promised much but did not do even a little [i.e., he promised the cave as a gift but took a great deal of money for it], for he took from him large shekels, viz. centenaria [worth one hundred smaller shekels], as it is stated:“accepted by the merchant,” i.e., they are accepted as a [full] shekel everywhere, for some places have large shekels, viz. centenaria, centeniers or zenteniyers in Old French,(hundred-unit weights.) -
Expanding the answer:
The OP asked "(1) Is that spelling change intentional? (2) If so, what message is being sent?".
The answers are: (1) Yes.
(2) Earlier in the narrative, Ephron promised the cave as a gift (his apparent generosity acknowledged with the full spelling of his name) , verse 11
"No, my lord, listen to me. I have given you the field, and the cave that is in it, I have given it to you. Before the eyes of the sons of my people, I have given it to you; bury your dead."
but in the end took a great deal of money for it (the fact that he did not fulfill his earlier promise acknowledged with the defective spelling).
When the Tanak was first written, it was written without vowels. In the early Middle Ages (ca AD 800), scribes known as the Masoretes added the system of vowel points (niqqud or "diacretic markings") that are used in pointed Hebrew texts since then. Other systems were developed at roughly the same time (as Hebrew became less of a spoken language), but only the Masoretic system is used to any extent today.
Before the use of niqqud, a system of differentiating words came about that marked when a long vowel should be pronounced. This system, known today by the Latin name matres lectionis (i.e. "mothers of reading") uses certain consonants (aleph, he, yod, and waw) to mark where a long vowel would be and thus differentiate between words that otherwise would be spelt the same way. When a word is written using the full niqqud, it is called plene or male. If it is written without the niqqud, it is called haser or defective).
When the masoretes designed the niqqud, they made use of the mater. Aleph marked long a sometimes but kamets alone is more common. He marked e or long a. Waw marked tone-long o (holem-waw) and tone-long u (shurek). Yod marked long i (hirek-yod) and long e (Tcere-yod). However, Hebrew words could still be written without these marks. This is especially true regarding holem-waw (tone-long o) and tcere yod (long i). Both of those niqqud exist in full and defective forms. That is, both holem and holem-waw make the same sound as do tcere and tcere-yod.
As you mentioned, the pointed Hebrew text of Genesis 23:16 uses the full spelling of Ephron first (holem waw) and then the defective spelling (simply holem). The pronunciation is the same, and I would draw no conclusions from it (but them I'm neither Akiva nor Mitchell Dahood).
When I was new to studying the OT in Hebrew, the TV program "Ancient Jewish Wisdom" (Rabbi Lapin) opened the world of wonders of Hebrew to me - beyond language only.
These are my notes from the Ophrun/Ophrn TV program explanation:
vav - part of God's name - good sign. When it vanishes from the name, not so good.
Gen 23:8 – Ephron/Ophrun has vav.
In Gen. 23:15, Ophrun is two-faced and says that the land is worth 400 shekels of silver – but between me and you, what is that? Bury your dead!
Gen. 23:16 – And he (Abraham) is listening (Paying deeper attention, and sees Ophrun’s desire to appear magnanimous in front of others, yet truly desiring to be paid.) In same verse, Ophrun loses his ‘Godly vav’.
The field remained holy in v. 23:17; only the man had ‘shrunk’.
Since that time, I pay careful attention to ‘vav changes’.