One consequence could be that there might be less fan engagement in some ways. Fans who respected James Potter's (hypothetical) wishes might be less likely to create or support fanfiction. This could lead to a smaller body of fan - created work related to Harry.
Well, for Harry, he might grow up with a sense of abandonment. In some fanfictions, this could lead to him having trust issues or a longing to find out about his real parents. For example, he might struggle with his identity, not knowing why his parents gave him away.
One possible consequence could be a lot of chaos and panic among the students and residents. With Hogsmeade being a popular place for Hogwarts students to visit, an attack would surely terrify them. Some students might get separated from their friends or get injured. The safety of Hogwarts itself could also be in jeopardy as Hogsmeade is so close. The local businesses in Hogsmeade would likely suffer great losses, and it might take a long time for the place to recover its former charm and prosperity.
Well, it could be quite embarrassing for him. His friends might tease him a bit. And in the wizarding world, it might be seen as a rather odd thing to do, perhaps leading to some strange looks from other wizards.
The plot could involve the two of them having different magical abilities despite being twins. Harry might inherit more of his mother's protection magic while James could have some other unique power. They could also have different relationships with Sirius, with Sirius perhaps being more protective of both of them. And when they go to Hogwarts, they could have different reactions to the Sorting Hat. James might be sorted into Gryffindor right away, but Harry could be a Hat - stall between Gryffindor and another house, which could create an interesting story arc about his identity and loyalties.
The abuser could face magical justice. In the wizarding world, there are probably spells or enchantments that can be used to punish wrongdoers. James Potter might use his connections to ensure the abuser is dealt with severely, like being sent to Azkaban or having their magic restricted.
One possible consequence could be a moral breakdown within Harry himself. He's always been against dark magic, so using Crucio might make him question his own values. Another consequence could be alienation from his friends and allies. They would likely be shocked and appalled that he resorted to such a cruel curse.
In fanfiction, if a Harry Potter wand exploded, it might lead to the wizard losing their magical abilities for a while. Since the wand is the conduit for magic, its explosion could sever the connection temporarily.
If Harry Potter makes a Horcrux in fanfiction, it would be a major departure from his character. Horcruxes are dark magic, and Harry is firmly on the side of good. One consequence could be that he starts to be corrupted by the dark magic within the Horcrux. His friends might turn against him as they see him slipping into darkness. He could also lose his connection to the positive magic that has always defined him, like his ability to use the Patronus charm.
She could play the role of a new friend. For example, she might be a transfer student from a different wizarding school who befriends Harry and helps him in his fight against the dark forces. Maybe she has some unique magical abilities that give an edge in battles.
In a Harry Potter and James Bond crossover, it might start with Bond investigating some strange disappearances that are actually the work of a rogue wizard. He stumbles upon the wizarding world and is initially out of his depth. However, with the help of Hermione, who is fascinated by his technology, they start to figure out a way to stop the wizard. Bond's skills in combat and espionage combined with Hermione's magical knowledge make for an interesting dynamic.