Indeed not; it's way quicker and easier than a bicycle. Deflate tyre, undo the handful of bolts which hold the 2 halves of the rim together, swap tube, bolt back together, inflate, done. Takes longer to remove the wheel from the aircraft than it does to actually change a tube or tyre!
Ah, no. Its really not that simple. Hence the reason why you really shouldn't be doing it unless you know what you're doing and have the current publication, proper materials,and appropriate tools in hand.