If 'harry potter is accelerator fanfiction' was true, it would be a radical departure from what we know of the 'Harry Potter' story. The magical world of 'Harry Potter' would be infused with elements from the Accelerator world. Maybe the wizards would have some of the powers or characteristics of Accelerator. The storylines would change completely. Instead of the familiar battles against the Dark Arts in 'Harry Potter', there could be battles based on the concepts from Accelerator. It would also mean that the original themes of friendship, courage, and the fight against evil in 'Harry Potter' would be overshadowed or re - interpreted in the light of Accelerator's concepts. But this is a very unlikely and almost absurd concept considering their independent origins.
If that were true, it would be a very strange and unlikely scenario. It would imply that the 'Harry Potter' series was created as a derivative work of the Accelerator concept. This would mean that all the elements we know in 'Harry Potter' like the Hogwarts houses, the Ministry of Magic, and the Deathly Hallows would be somehow related to or inspired by Accelerator. It could also mean that the characters' personalities and motives would be adjusted according to the Accelerator - based concepts. However, considering the vast differences between the two, it's hard to imagine how this could be possible.
If it were true, it would mean a complete overhaul of the 'Harry Potter' universe. The magic in 'Harry Potter' would likely be mixed with the concepts related to Accelerator. For example, the spells and potions in 'Harry Potter' might be replaced or combined with the powers that Accelerator has. Characters would also change drastically. Harry might gain some of Accelerator's abilities, and the story would probably shift from a fight against Voldemort to something related to the threats in the Accelerator's world. But this is all very far - fetched as they are two very different fictional entities.