Background Changes for Harry
First, Harry can spend equal amounts of time learning things and keeping up with things in the muggle world along with the wizard world.
Dumbledore also never tells Harry about the Blood protection from his mother.
He’ll also have a tendency to walk around, partly because of how often he was in enclosed spaces while growing up. This will be both at Hogwarts after hours and in the Muggle World, like with Harry taking the bus to the city or hanging out alone in Little Whinging. He can also convert some of his money to pounds to use for emergencies. Harry buys a cell phone during the summer before fourth year.
Lastly, Harry will be more open-minded, like in the fanfic Protection from Nargles, and less shallow than in canon. On a side note, Luna will also have a sense of humor, but it will come out when you get to know her (inspired by Protection from Nargles).