Yaarel
🇮🇱 🇺🇦 He-Mage
That is player preference for the character concept, or the DM concept for the community.I think you are getting closer at this point, but the ability to 'adapt' on level in such a manner, isnt something I would incorporate.
For example, a player might have the character gain the Darkvision 120, and leave it at that for the rest of the life. Or take the Telepathy and be done.
Also, swapping only when leveling or feating encourages a commitment.
The Elf descends from mercurial shapeshifters. That there are moments of profound shapeshifting during the life of an Elf, is innate.