I wonder if he has to fight his tendency to be prickly or get creative with it just so he can say the things he wants to say. He ends up sounding like a tsundere all the time because of it.
I remember him taking issue with it like he's just commandeering a character with a preexisting personality, but now, it just sounds like it's all him.
He has been in that body for a bunch of years already, so I reckon much fusing is inevitable. That being said, it would be only now that he could really change, if he wanted to change, due to being free from his terrible household and also realising he needs to rely on others if he really wants to change the story in a favourable direction. Before this incident he still firmly believed he's much better off keeping maximum distance to other people, especially emotionally, only cooperating with them for the sake of specific tasks (like the whole agricultural thing), nothing more. That belief would have reduced his motivation to try to fix the original Harold's foul mouth. It served his purposes, after all, despite annoying him greatly. It especially served him with Erika, as he believed he absolutely must make her hate him, otherwise she wouldn't end up in the hero's party.