One good small change could be in the character development. For example, Neville could start showing his courage a bit earlier in the fanfiction. This would add an interesting twist as it would make the story deviate slightly from the original in a positive way. It could also change the dynamics within the group of friends at Hogwarts.
In some fanfiction, Harry changes his life by changing his attitude towards his enemies. Instead of always being on the defensive, he tries to understand them. For instance, he might reach out to some of the children of Death Eaters and tries to show them a different path. This not only changes his relationship with his former foes but also earns him respect from both sides of the conflict. It also changes the way the wizarding world perceives him, from a simple hero to a peacemaker.
Some Harry Potter - focused forums may also have users sharing their 'harry changes fanfiction'. These can be a bit more niche and might require some digging around, but you could find some unique and interesting stories that way.
One popular 'harry changes fanfiction' could be those where Harry's personality changes due to a magical accident. For example, he might become more confident and outspoken. Another type could be where he changes his appearance through a new spell and how that affects his relationships at Hogwarts.
In fanfiction, Harry might change the social structure at Hogwarts. He could encourage more friendships across house boundaries. By doing so, he breaks down the long - standing barriers between the houses. This would lead to a more harmonious and collaborative environment at the school, with students from all houses working together on projects and sharing knowledge.
Well, in a lot of Petunia and Harry fanfictions, an alteration can be how their pasts are connected. Some fanfics might explore if Petunia had some sort of latent magical ability that she hid, and this could change how she views Harry's magic. It could also lead to her teaching Harry things about magic that she learned in her own way. Regarding Harry, his view of the Muggle world through Petunia could be different. He might come to understand and appreciate the Muggle side of his family more deeply, which is a big alteration from the original story where he was often at odds with the Dursleys.
In fanfiction, 'Harry Potter changes Westeros' could be through his magic skills. For example, his spells like Wingardium Leviosa could be used to move heavy objects in Westeros, which might change the way battles are fought or construction is done. His knowledge of the magical world could also introduce new concepts to the people of Westeros.
He could make friends with a shy but extremely talented wizard who has been overlooked by others. Maybe a girl who is really good at potion - making but is too introverted to show off her skills. Another new friend could be a joker - type character who always lightens the mood with his funny magic tricks. And there might be a tough - looking guy who is actually a big softie inside and becomes Harry's loyal friend.
In the fanfic, there might be changes in the security measures of Azkaban. For example, new spells or wards could be added to prevent prisoners from escaping more effectively.
Often, he becomes more self - reliant. Since he can't always count on others during the summer away from Hogwarts, he learns to solve problems on his own. For instance, if there's a magical creature causing trouble near the Dursleys' house, he has to figure out how to deal with it without the help of teachers or friends right away.