I really hate when isekai MCs acknowledge something as being broken cheat magic / secret player knowledge / whatever, and then when people correctly freak out when they use it, they just go "ehhh~ I was just using this change magic, you know?" like they think it's common.
If he was legitimately clueless about how OP he is (like some MCs are) it'd be one thing, but he established beforehand how this was a broken skill he only knew because of his past knowledge, and it was a spell learned from late-game enemies. He has no reason to pull that shit.