I decided not to try moving the piston pivot hole. Instead I drilled a 2mm hole in the top of the cylinder, 4.5cm from the front end and carefully smoothed out the inside of the hole. The piston then only compresses air after it passes this hole. The cocking stroke is now much easier and the power doesn't seem to be much less. Accuracy is the same, and the pistol still knocks over cans at 12 metres. If I want to go back to the full power setting, all I need to do is cover the 2mm hole with some self-adhesive aluminium tape.