I've always liked to double check the derailleur adjustment when swapping wheels.
However, if you have the same brand/model of hubs and cassettes, then the changeover should be easy enough. The size of the sprockets shouldn't make a huge difference as long as your chain works with the largest cassette.
If you have tire clearance, and have DISC brakes, then you may be able to use both 650b and 700c on the same bike.