...it might still be a lot of work isnt it ?
I've never edited map areas myself, so I could be completely wrong on this, but from what I've heard, simply adding doors and similar transitions from one area to another are pretty easy. You just find an
existing door that looks pretty much what you want the new door to look like (same size & shape, angle to the viewer, etc.), copy that image, and slap it where you want the door to be. Then you edit the "trigger layer" of the map, so that when you mouse-over that spot, the pointer changes to the "Door Here" pointer, etc., and you tell the program what area file that door leads to. There's already been at least one mod that does this: it takes the building just north of the Copper Coronet and makes it accessible to the player (it's some kind of Dwarf-themed Inn), although I haven't seen any reviews.
I'm not sure what happens if two different mods edit the same map area. I expect that the newer one will simply overwrite the older.