I first posted this here, at Mi Yodeya, but they seem to feel it's off-topic. Happily for me, someone still gave an answer that allowed me to improve the question considerably. I've adapted the question somewhat for this site.
The Dead Sea Scrolls (DSS) version of Isaiah permits us to read Isaiah 52:14 as describing a servant whose appearance was 'anointed' beyond human semblance, rather than the familiar 'marred'. The Targum seems to support this, and early Christians saw the servant as a prophecy of the Messiah (i.e. the anointed one). Should we prefer this reading?
English translations of Isaiah 52, based on the Hebrew of the Masoretic Text (MT), describe the servant as 'marred', or similar.
Just as many were appalled at you, My people, So His appearance was marred beyond that of a man, And His form beyond the sons of mankind.
כַּאֲשֶׁ֨ר שָׁמְמ֤וּ עָלֶ֙יךָ֙ רַבִּ֔ים כֵּן־מִשְׁחַ֥ת מֵאִ֖ישׁ מַרְאֵ֑הוּ וְתֹאֲר֖וֹ מִבְּנֵ֥י אָדָֽם
The word translated as 'marred' is מִשְׁחַת = MIShḤAT. The Great Isaiah Scroll (GIS) found at Qumran has one extra letter at the end of this word compared to the MT, making משחתי, which could be read either as MIShḤAT = 'marred' again, or as MAShAḤTI = 'I anointed'.
Isaiah 52:14 (NASB, modified by me)
Just as many were appalled at you, My people, So His appearance I anointed beyond that of a man, And His form beyond the sons of mankind.
This reading appears to be supported by the Targum Jonathan (TJ; a First Century CE Aramaic paraphrase) version of the previous verse, which identifies the servant as the Messiah/anointed one.
Behold, my servant the Messiah shall prosper, He shall be exalted and extolled, and He shall be very strong.
הָא יַצְלַח עַבְדִי מְשִׁיחָא יְרוּם וְיִסְגֵי וְיִתְקוֹף לַחֲדָא
To anoint someone's appearance beyond that of a human seems to imply glorification, and this also seems to be supported by the Targum.
His visage shall not be the visage of a common person, neither His fear the fear of a plebeian; but a holy brightness shall be His brightness, that everyone who seeth Him shall contemplate Him.
בְּכֵן יְהֵי לְבוּסְרָן וְיִפְסִיק יְקָר כָּל מַלְכְּוָתָא יְהוֹן חֲלָשִׁין וְדָוָן הָא כֶּאֱנַשׁ כֵּיבִין וּמְזוּמַן לְמַרְעִין וּכְמָא דַהֲוַת מְסַלְקָא אַפֵּי שְׁכִנְתָּא מִנָנָא בְסִירִין וְלָא חֲשִׁיבִין
This question is prompted by reading Margaret Barker's book, Temple Mysticism - An Introduction (ISBN-13: 978-0281056347).
Caveats and acknowledgements
I don't read Hebrew or Aramaic and haven't read the Targum extensively. I relied on copy-and-paste to quote Hebrew script so, while I tried to copy accurately, I'm unlikely to spot any mistakes I made. Transliterations are from the erudite answer of Mi Yodeya user magicker72, to whom I'm indebted. The original research is Barker's. I of course recognise that the Targum is not canonical, and use it only as a source of insight into how 1st Century Jews understood Isaiah.