It's working fine for me, I just rarely need its features so I thought I'd lighten the mod load a little bit. But since it replaces the regular beds with its custom objects, how do I remove the mod safely/without accidentally nuking any sleeping Sims?

This isn't a question that comes up very often because the mod is so lightweight and typically harmless. All it really does is tamper with the OBJK resources of double beds, and only base game and EP/SP models, that come into existence in-game while/after the mod is present. Custom and Store Content double beds are exempted unless the player has changed those objects to match themselves.

If you remove the mod from an ongoing game that has used it, then any beds so affected will disappear entirely. So will any sims using them at the time, I believe for any purpose. The beds would have to be replaced, the sims should be retrievable by way of ErrorTrap restoring them (I think or maybe it's Overwatch) or the households may need to then be fixed manually, but I wouldn't recommend going that route.

If the mod isn't causing problems, honestly I would just leave it be for a world that has already made extensive use of it. It can't be causing that much overhead, at least I don't think it would. Perhaps a couple of seconds on the startup time? But it you must, I would say that a MC Reset Everything run from the Town Menu on City Hall first would help ensure that no beds are being used for the moment since doing that resets all sims in the world no matter what they were busy doing at the time. Then a save (as), quit, and reload without the mod present and the caches cleared, in the hopes that no sims in town manage to jump back into a bed that is no longer there all of a sudden.