Isn't that the point though? You know as much as your character knows about the other person's power, so it would be both of you learning to use the powers. Besides, I'm not sure about everybody else, but I for one wouldn't care if you messed up Data's powers (which are staying with his body anyway, remember?), as long as you do iy in a plausable way.
Data has a limited amount of magical ability for himself, and might have a "SUPER SECRET BONUS POWER" that he doesn't know about. But it'll be funny to see Data as a semi normal human girl, especially if he starts to accept his role.