You could probably recreate the main campaign as empty levels, eliminate all the scripts but use existing NPCs and stuff and then the GM could give a new personality for all the characters and completely change the feel of fort joy (e.g., add more guards and prisoners, make a bunch of voidwoken attack, etc). Not ideal, but could be fun with the right group of people and GM.
Even that won't really work.
I was told by a dev at steam that "same level area transations" such as to the cave with the elves and the interior of the Fort won't work because of that being scripting. Therefor you may asume that "atmosphere triggers" won't work either.
Of course the GM can change the atmosphere. but that will be "level wide" so player(s) not in an interior will also have the interior lighting, or the player(s) inside will have exterior lighting.
It looks like the GM mode really forces you to run a campaign as a series of encounters in small areas unless you are willing to suffer long loading times every time the party leaves an interior like a shop and goes outside to the "large exterior".
Some limited scripting, such as same level transitions and atmosphere triggers are a must if you ask me as they will hugly expand the experience and actually allow for larger areas instead of forcing the GM to stick to small encounter based ones.
