I actually think it would be much easier to just remove all lines referring to the First Order stormtroopers being taken as children. I think it was just a few lines in TFA that mentioned it, so it should be pretty easy. It would make Finn’s decision to leave seem more unique, as if he was one of the few troopers who didn’t support genocidal fascism. It would also make it less weird that he kills his former comrades without a second thought.
That’s a good idea too. Plus, I feel like knowing that he, at some point, chose to enlist in the First Order would make him feel like he has more of a character.