Talk about radical nerds. Lab coat... >o> Anyways, it's the first game I've ever heard they change of clothes, pherhaps they also take baths to increase their growth?
Kairi changed her clothes. Sora did too. And Riku. It's not uncommon. Sure they can take baths, eat food, and pee to make them feel "Great"
But all Persona-ness aside, the characters are known to change their clothes.