Harry might be more open - minded. The Delacour family has connections to the wider wizarding world outside of Britain. He would be exposed to different cultures, magics, and ways of thinking. This would likely make him more accepting of new ideas and less likely to be bound by the traditional British wizarding ways. He could be more adventurous in exploring different magical practices and making friends from all over the world.
His confidence could be boosted in different ways. Growing up in a family like the Delacours, he would be constantly surrounded by people with a certain level of magical prowess. This might make him more self - assured in his own abilities, not in the sense of bravado but more of a quiet confidence. He may not have the same insecurities he had in the original story.
He'd probably be more sophisticated. The Delacour family is known for their elegance and grace. Harry might have a more refined way of speaking and acting compared to his canon self. For instance, he would be more likely to use formal French wizarding greetings.