Advice on Changing Pads in a Parking lot

Leave the caliper alone, you don't hafta remove it from the spindle, or top of the rotor.
Remove the pad hold down clips, on top of the caliper.
Get out a big, decent sized screwdriver to use as a pry bar.
Pry between pad side and the rotor.
Push the pistons on that side back into their bores, fully.
Install that side brake pade that you just took out.
Do the same thing to the second pad in the caliper.
Easy, peasy, to just repad one of those brake systems.

Let me add, DON'T bust those little 1/4 inch diameter bolts, that hold the pad hold down clips in place.
Then your really going to be screwed, up ***** creek, without a paddle, in a strong head wind.
You then won't have any way to keep the pads in place.