yes, you can adjust the preload for a couple of psi, but if there is too little or too much preload the w/g wont work as it should (leakage or boost creep) you should choose the actuator psi for your minimum, then make adjustment via a controller ideally
the spring that i fitted works against the w/g internal spring (so a 10kg internal spring with a 5 kg spring pushing against it drops the pull from 10 down to 5)