"is it possible to "reset" the fog of war in a particular map, like the dark forest?"
For the Dark Forest, replace the shroud.x2 file in the saved game folder with a copy from the '..\Divine Divinity\Run\main\startup.v2' folder (or '..\main\startup' if you do not have the 1.34 patch installed).
I checked that this would work, but don't know if there would be any other consequences. Probably not, but try this in a new save in case there are problems.
.x0 = Aleroth, Ars magicana, etc.
.x1 = Verdistis, council hall
