I have a character who was originally OU but would be an AU version because of changes after returning to their home world after a previous game. How would I go about apping them?

Would this be an AU app with the current AU, then working with mods to get the previous game memories back after their first AC?

Would it be best to app as OU and work with mods for a combined canon update into the AU alongside the previous game memories later? Is that possible?