Questions about baking mult. ver. of mult. lightmaps

In my game, you walk around in this building.
This building is split into 5 areas.
In each area, you can turn the power on and off, which in turn changes the lighting.
You can have power in one area, and not another, so the lightmaps need to change independently.
That means each area needs its own lightmap, and two different versions.

Now how in the heck would I do the following:
- Bake only a section of the map (one area)
- Bake a second lightmap in an area without overriding the original
- Load in the lightmaps (although I believe I would use LightmapSnapshots)

I could use only realtime lighting, but that would kill performance and baked lighting looks much better anyways.
Thanks

EDIT:
I'm just gonna remove the power mechanic and keep everything baked.