Well I've got switchable/random skydomes and fx files to work (in much the same way as space maps do it). However, I can't seem to get lighting (LGT files) to switch with them. What I've tried so far is:
1) Load LGT files along with sky files+fx files in the same method the space skies use. No effect.
2) Create two seperate layers in ZE with different lighting. Load only 1. If the base layer's LGT file is removed they have no effect, if it's still their then no effect.

Anyone got any ideas how to get around this?
My current best idea is to use fx/sky files to modify world brightness/contrast, although I'm not sure exactly what parameters to use.

Not sure if this will help you at all but I do know that each .lyr file has a line in it to call for a .lgt file so theoretically you could load a different lgt per mode but I am not sure about being random.

Yeah I tried that....but the map just uses the base layer's lighting, and if that gets removed it just uses no lighting.

You have lgt calls in the lyr but not in the base? Any other lgt being called?
I can't remember if I got that to work ever... I'm not sure if I settled on using .fx's and shadow regions instead ...

Nope no other lights being called....
Don't suppose you remember how you got it to work with fx and shadowregions?

Not totally sure where you want to go with this, but did some playing and all spot, omni and directional lights can be on different mode layers and can be different colors, locations etc.
If you copy the Global light settings from the map.lgt file to the mode.lgt file and change the top and bottom colors that also works it didn't seem to change the ambient light though still have to work on that one.
Here is a picture of two modes, conquest and assault same location different color omni lights.
Pictures we darkened a bit so the colors showed up better but that is all that was changed.