You can't edit the lived in apartments once the new residents move in, so it would need to be done beforehand. Not sure about tips... I've been playing with for rent in my main save with no issues since the release. I haven't done anything special, I think perhaps it's just not that common bug (although very serious).
I love your setup btw. I played villanous valentine aspiration in my legacy save in a similar way. Because I didn't have any couples left to break up in the normal save, I made a new save that was him dreaming and getting the aspiration done, breaking up the premade couples.