Re: How do I set a sim's party costume?

There isn't a CAS section for that. What I've done when I want to customize is to add the costumes I want to one of the regular options, change their outfits in live play if I don't like the ones the game puts on them (I've got a change non-played Sims clothes mod), and then delete the costumes later. Which means I've not done it a lot.