Yes, but not with an unmodified toolkit, which opens levels as read-only, and disallows creating new levels. But there is a patch for the toolkit on nexusmods which unlocks the toolkit and makes the map editor and other stuff available. If you know what you are doing, you should be able to edit the main campaign or make your own.

I played around with it a bit, and all I can say, its complicated.

That's what I want out of the game, really. A full toolkit a la Neverwinter Nights.

Read through the documentation of their newly released modding toolkit and find out, I guess.