I wonder... that would have been very interesting if they could shapeshit at will. However I have noticed that when naga become those monstrosities, they do somehow revert to their night elven form, also noticed Queen Azshara's emissaries are all night elven females (if it is a lore thing and they look more like copies.).
I know Azshara can shift at will, I wonder if the naga actually much prefer and like their naga appearances, pretty much like the Eredar Man'ari preferred their twisted engorged visages, and if they could turn at will, they find it inferior. No indication of that at all, just wondering.
Secondly..
We know that night elves can still turn into Satyr, even against their will
Last I checked the debate was still raging if night elves can still turn into high elves. Did they ever resolve that? Last I checked, when a rogue night elf was caught breaking the ban on the arcane, he was severed from his connections and exiled, becoming a high elf (in appearance at least), we were debating this 11 years ago, but I quit wow for a while , so not sure it got resolrved.
Without the nightwell, night elves can't turn into nightborne.
However there have been no cases of the reverse. Except for Elune turning some satyrs back to night elves. night elf to high elf transitions looks permanent, but as an induced event, it might be possible this is still going on