If you are swapping in complete doors (full electrics, glass, all that), it should be very simple. Just unpin the doors, the check and the harness and swap away.
It would be more work by quite a bit if you had to swap the door guts as well, especially the window lifts as I recall they are riveted to the door.
Either way it's doable...just how much work do you want to put in.
Jeff
90 535i
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy