That must be backwards of the way the hydro pump reliefs work.
Either that or whoever wrote that is wrong...I can't envision how you would make a relief valve in which you would remove shims to increase the pressure. That seems counter-intuitive. If the relief valve is a plug with a spring and cone- or ball-shaped plunger under it, you will need to remove shims and not add them.
Now you've got me really curious as to how the relief valve in it is designed.
Do you have a GM pump or some other brand? I googled around and found that a lot of other PS pumps have a relief valve more like what the hydrostatic pumps use, where you'd remove shims to decrease the pressure.