They should just slip a new actor into Flashpoint during some timey wimey ****ery and say he changed because of timeline shenanigans. That way they can change him as much as they want, hell even his costume could change. Of course, a big question is when they would have the change occur. Ideally they would have it occur as soon as possible, but it depends on how much they're willing to chop up and alter existing footage. I assume they'd want the change to occur more towards the end. But if they plan (haha, having a plan, what a concept) on using this version of Flash in the future it would benefit them to at least have the new actor appear before the climax so people have a reason to feel more hyped about seeing more of this portrayal.