that would be quite difficult i use a similar thing in my game:
there are a few classes and you chose one to be in during the beggining:
use a show choices command with the classes:
choice 1: ninja
change the sprite accociation for the main character to the ninja sprite
choice 2: mage
choice 3 gunner
choice4:more
show choices again
choice 1
etc.
hope that made some sense