Pump pressure is controlled by the spring that pushes the diaphragm after the cam lobe and lever compresses it. Installing a spring with less tension would be the logical way to reduce the pressure. Shortening a spring doesn't reduce its strength- - - - -if anything, it would increase the tension. Someone would need to find a spring approximately the same free length as original, with smaller diameter coil wire for less push.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!