Absolutely! Some role-plays allow made-up characters, others prefer to keep it canon-based; it really depends on the RP itself and it's creator, but yes. In Knockturn Alley (RPG) you CAN use your School and/or Ministry character if you wish to, but no you do not HAVE use either; you're free to use whatever character you like, as long as the creator of the RP in question approves and you are role-playing for your character and not someone elses.

Most commonly, the RP thread creator will ask that the members who join post their character's bio in the thread before the actual RPing begins, but we do have a thread in KA for members to save their characters bio's (all in ONE post, as the thread states ) which you can find here: Character Archives.