We have some evidence Harry has defense professor permissions and didn't trip any wards because of that. He practiced memory charms. In Hogwarts. If the castle thought of him as a student, that would have set alarms ringing, with professor permissions, no alarms. Not strong evidence, because Harry was Dumbledores pet disaster, and it is entirely possible he'd hear an alarm like that, check up on what Harry was doing, and ignore it as long as he wasn't casting it on students. But it's an implication.