Hey,
Love your story and the way you portray Harry. With Harry as being as intelligent as he is he must be aware that he can get away with pretty much anything he wants without fear of being expelled since Dumbledore made such an effort to get him there in the first place. Now in the muggle world it hasn't been in Harry's character to misbehave because he has been trying to get ahead but will his new situation cause him to do what he wants to and not follow the rules since he knows that nothing can happen to him. I mean if he does something to give him a detention he can merely skip it with no consequence. They either expel him which he must know they wont do and even if they did would allow him to go back to the muggle world or they just do nothing. If I was Harry I would use that to my upmost advantage.