Well, in a fanfiction where Harry Potter becomes god, the whole concept of Hogwarts and magic education could change. He might make Hogwarts a place where every student can reach their full potential without any limitations. There would be no more house rivalries as he could instill a sense of unity in all the students. He could also create new magical creatures or bring back extinct ones, like the phoenix in large numbers, to make the magical world more vibrant and diverse.
If Harry Potter becomes god in fanfiction, he might completely reshape the magical world. He could rewrite the laws of magic, perhaps making it more accessible and less dangerous. He could also bestow extraordinary gifts upon his friends. Hermione might gain the ability to instantly understand and master any spell or bit of knowledge, and Ron could become an unbeatable warrior with superhuman strength in the face of any danger.
He could have ultimate power to change the wizarding world completely. For example, he could end all forms of dark magic forever and bring eternal peace. He might also be able to resurrect those who died in the fight against Voldemort.
Well, he might gain incredible powers like the Greek gods. He could control the elements, for example, just like Zeus controls lightning. Maybe he'd also have a new look, with a more god - like appearance. And his relationships would change too. His friends might view him differently, with a mix of awe and perhaps a bit of fear.
Well, he could probably change a lot of things. He might go back in time and prevent some of the tragedies that happened in the original story, like the death of his parents. As a god, he would have incredible powers, so he could easily defeat Voldemort much earlier and save a lot of lives. Maybe he would also use his newfound god - like status to bring about a more just and equal wizarding world.
Well, in such a fanfiction, Harry might gain incredible powers of destruction. He could start to reshape the magical world according to his newfound, perhaps more radical, ideas. Maybe he would use his powers to destroy dark magic at its roots, but also accidentally cause some chaos in the process as he's still learning to control this new god - like power.
In some fanfictions, if Harry Potter becomes a warlock, he might gain even more powerful magic. He could have greater control over spells and be able to perform magic that was previously thought impossible. For example, he might be able to manipulate time in a more complex way or have the power to instantly transport himself anywhere in the wizarding world without the need for a Portkey or Apparition.
In this kind of fanfiction, Harry might teach his children magic in a very different way from how he was taught. He would be extremely protective, having faced so many dangers himself. Maybe he'd pass on the lessons he learned from his own battles, like the importance of friendship and courage.
If Harry Potter becomes the Joker in fanfiction, he would probably start to question all the values he once held. The Joker is all about subverting order, so Harry might begin to undermine the Ministry of Magic and other institutions. He could use his knowledge of magic to play cruel pranks on people, not the innocent kind of pranks he used to do. His Gryffindor courage could be twisted into a reckless disregard for the safety of others.
If Harry Potter becomes a Jedi, he would likely combine his existing magical skills with Jedi abilities. His Patronus charm could be enhanced by the Force, becoming an even more powerful protective entity. He might use his wand as a sort of lightsaber hilt, channeling the Force through it for unique combat moves. His ability to apparate could be refined with Jedi - like teleportation skills. Also, his knowledge of the wizarding world's dark magic could help him better understand the dark side of the Force and avoid its temptations.
If Harry Potter becomes a Lamia in fanfiction, his relationships would change drastically. His friends might be both intrigued and a bit scared at first. He would have to adapt to his new form and its characteristics. For example, he may need to learn how to control any new instincts that come with being a Lamia. Also, his role in the fight against Voldemort could be completely different. Instead of using a wand in the traditional way, he could use his Lamia - related powers to combat the dark forces.
If Harry Potter becomes a demon in fanfiction, his relationships would be severely affected. His friends like Ron and Hermione would be very confused and possibly afraid of him. They might try to find a way to reverse the transformation. And Hogwarts itself would be in chaos. The teachers would be divided on how to deal with him, some might want to help him while others might see him as a threat to the safety of the school.