Adding additional form with trait

Hello, I’m working on creating a trait (with Sims4Studio and Zerbu) and was wondering if I could add an additional form to those who have that trait. Just like how the mermaids have their human and mermaid forms, vampires have the dark form, aliens’ disguises etc.

(Ideally having it unlocked so you don’t have the restrictions to the same body type etc, but I know that may not be possible.)

Does someone have a suggestion of how I could do that? Any help is appreciated.