Yes,it is straightforward.
It helps to have compressed air. Use either a block of wood or the old brake pad to catch the piston and use compressed air to blow the piston out of the caliper. Apply the air through the hose attaching hole.
It also helps to use compressed air to reinstall the piston.
While the piston is out, clean the bore with brake clean and a lint free rag. Replace the square cut "O" ring on the piston. Replace the boot seal on the caliper. Liberally lubricate the piston, bore, and lips of the seals with FRESH BRAKE FLUID. With the help of an assistant if needed, apply compressed air gently through the hose attaching hole while holding the piston right above the bore. When you get the pressure just right and hold the piston just right, the piston will slide right in as the boot swells out around it.
Do your best to at least find compressed air to blow the piston out. It usually is difficult to get it out without. With patience and strong hands you may be able to twist and rock the piston until it comes out.
Without compressed air, the piston can be reinserted using a bent paperclip to slide around the piston and pull the boot away just enough to get the piston through. It may help to cock the piston to one side while engaging the boot but before hitting the bore.
Have fun.
