is there a way to add custom assets and stuff such as custom shirts, hair, etc? if there is could someone please help out and if not, that would be an amazing feature to add in a future update, thankies! qwp

You kinda can using the custom items tab (the Star tab). And enabling jiggle mode, to make hair jiggle, for example. It may not be as detailed as the built-in stuff but it can get the job done