Swapping the .ml file

#1 Eeeew.

If you're looking to make dynamic terrain shadows, swapping the light maps causes the engine to stutter in a way that makes it unusable. It's just not practical in any implementation that I've seen or heard of on these forums in the 4 years I've been working with the engine.

If you're looking to simply affect the light map with different effects, that is a different matter. I just went through something similar with my day/night code.

I simply modified the light map in real-time as opposed to swapping in another one. The trick is to make sure that you are altering the light map for all objects in the scene by the same intensity. The sticky part is that each object type has it's own way of rendering light maps which requires you to make alterations throughout the engine.