As always, I'm afraid to break the game, moreover, I'm afraid to detect a breakage far from immediately, so I want to consult with knowledgeable players. What happens if I assign a sim from an active family to a position as a role-sim? I've successfully assigned residents instead of homeless sims, but I've never done anything like this with an active family.

The game won't break, but it's not expected that the sim's role assignment will be or remain stable.

igazor, in all other cases, role-sims work stably, even if they have a strange desire to leave their post. Well, okay, if it really doesn't cause a time bomb in my game, I'm willing to experiment. But I'll definitely let you know if I get some very unexpected result

If they don't lose their role assignments entirely, you will most likely find that they do not consistently staff their objects and that there are no commands available to make them do so.