While compressing piston in rear caliper to spin it also?

It is if it uses the caliper as the parking brake as yours does. The reason for that is that the parking brake is based on a threaded rod that rod engages threads inside the piston that pushes it out when the parking brake cable moves the lever on the rear of the caliper. In order to push the piston in it has to be rotated to screw it back down onto that threaded rod. If you just try to compress it with a C-Clamp or similar tool it will damage the piston and caliper and now you have to replace it because it likely will not work in either the parking brake or the hydraulic braking modes it normally operates in with the damage that it does to the piston.
Using the correct tool you squeeze and rotate the piston at the same time and that resets the caliper so the new pads will fit. Be sure that when the piston is fully compressed you rotate it so that the slots in it line up with the pins on the rear of the pad. That keeps the piston from rotating when the park brake is applied.

https://www.2carpros.com/articles/how-to-replace-rear-brake-pads-and-rotors

You can generally get the tool required as a loaner tool from a parts store, or if you plan on doing brakes on a few vehicles the Astro 78618 covers pretty much all of the current styles that that are out there with the cable operated brakes, doesn't work for the newer electronic parking brakes though.