*does some in game testing*
Yes, there is. All female mannequins share one CAS slot, but you can set multiple outfits by making them in CAS. When you design an outfit for a sim, at the very top of the clothing selection there are little tabs for making more outfits.
Like this!
Then when you go to dress your mannequins it'll ask which outfit you want. So fill out all the outfit slots in all the categories for maximum options!