Front or rear? You never NEED a c-clamp to retract a piston. If you do, the piston is sticking and the caliper must be replaced or rebuilt. On the front, I just use a small flat-blade screwdriver to pry the piston back before I unbolt the caliper. If it won't work that way, I know I need to take it apart to clean it out and rebuild it.
On the rear, you need the special tool if the parking brake is built into the caliper. If the parking brake is a separate drum brake inside the rotor, you treat the calipers the same as the front ones.