Posted by AnonymousThere is a character_ui_db file in the parameters folder under your region folder (en_us for me). Sorry I don't have a link for it, but there is a tutorial for it. There is a value that tells the game to only have 8 slots. You can change this value to have extra slots.
Does having more than eight alternate costumes require a mod of some sort? Because when I put shadow mario in c09, it didn't work for me