Update on this. Not only did they let me switch, but they also treated me super nicely. They let me move to an empty economy x row, and have offered me a meal/snacks/drinks even though this was just a basic seat-only economy ticket. Each attendant has come up to me and asked me "if I'm the one that switched business class seats" haha. They told my partner that if he hasn't already, he should put a ring on it clearly this doesn't happen very often.