Can I swap one set of .030 over pistons for another, without machine work?

You can do the piston swap, measure skirts of the out going, and the incoming to get an idea of where you piston to wall clearance may fall. This will only be a measure of gaining or loosing clearance; buy some long pattern feeler gauges, slide one in along side a piston (with out the rings) in the hole. Your piston to wall will be 1/2 the feeler gauge. Use a "Blueberry"/ "Dingle Ball" hone for new rings; IF you wanted to try reusing what you have, don't touch the walls. Just make sure you gap the top ring per KB specs.

Balance your assembly.