What principle should be invented/concocted so that it should be "changed his glory" rather than "changed their glory"?
[כבודם] is plainly and simply 3rd person plural possessive.
We should be Bible fundamentalists and literalists and refrain from modifying the plain grammar of the Hebrew, because doing so would reflect a predisposed doctrine not found in the original Hebrew.
Such mode of interpretive-authoritative translation should stop.
Psalm 8 (my favourite passage to deride such an attitude/mode of translation):
- מה אנוש
- כי תזכרנו
- ובן אדם
- כי תפקדנו
- ותחסרהו מעט
- וכבוד והדר
However, people with a predisposed doctrine could not accept that Almighty Allah desires humankind to be nearly equal to Him. So they deliberately mistranslated the passage to reflect what you now find in KJV and NIV.
Another of my favourite and my oft overused passage to treat the indication of such masochistic mode of translation is Hosea 2:16 (Jewish enumeration = 2:18)
- והיה בים ההוא נאם יי
- then is existent that coming day declares the LORD
- תקראי אישׁי
- shall you call me my mensch-husband
- ולֹא תקראי לי עוד בעלי
- and not call me anymore my master-husband
Almighty Allah wants us humankind to be His equal.
When people translate the Bible this way, they are worshipping a golden calf. They invent a religion and debase themselves and refuse to accept that humankind is meant to be nearly equal to G'd.
They have already decided, this wonderful elegant golden calf perception of Almighty Allah is what you need. And here is the way we should mistranslate the scriptures, to reflect that predisposed golden calf we hewn out for you.