Generally speaking, it’s usually only Ksh’ta and terror/fear clans that slowly gain monstrous mutations. Most Cubi tend to just adjust to their mental idealized version of themselves (aka: they become more attractive) with a dash of whatever best suits their affinity. So joy clans tend to get more adorable, anger clans tend to look like they are always ready to handle a fight, lust clans…well you get the idea.
It’s a little bit different from actual shapeshifting in that it is actually altering their default look. (as been mentioned, if you knock a cubi out who has been shapeshifting they revert back to their default look) But it’s fairly slow and definitely not an overnight process, but tends to happen over the course of years after they start getting their Cubi powers. I think someone on one of the forums dubbed it ‘Cuberty’.