The AK gas piston can be replaced by using sand paper (the finer the better) to remove any paint, or bluing from the end of the carrier.
Next locate the center of the rivet holding the piston (it should go horizontal through the carrier)as close to center of the rivet as you can get make a center punch mark, then using a 1/8" drill, drill the flared end of the rivet off, then use a small punch or brad push out the rivet.
If the rivet doesn't move you may need to drill off the flared end on the other side. When the rivet is out unscrew the gas piston.
To install the new gas piston just screw it into the carrier until it stops, then unscrew it 1/2 to 3/4 turn, and using a drill the same size as the rivet drill through the gas piston at the rivet hole. If you are off a little you can drill from the other side.
Then remove the gas piston & drill out the gas piston's hole to the next size up (it should be about 1/8").
Reinstall the gas piston and screw all the way in, then back it out until the holes line up, then rivet it in. Flair out the rivet on both sides until it is equal & sand smooth, re-paint or re-blue. The gas piston should have a small amount of wobble to it, this is normal.