If you were doing different walls it wouldn't matter if it was on the same wall you would have two different bed depths, so that wouldn't work. I'm intrigued to know why you want to do this, have you broken a trowel?
I do a lot of commercial work, quite a bit of it is nights and unsociable hours. I always buy a couple of trowels at a time so I've always got a spare should something happen to one out of hours.