Adjusting pressure relief valve on well water
Most (or the ones I've met) well system pressure reliefs are non-adjustable. So if it leaks 30 PSI below rated pressure, I'd replace it (for less cost than your proposed tool purchase, as far as I recall.) Odds are that parts to rebuild yours will be more than simply buying a new one.

Toilet valves get wonky (or may) above 80 PSI or so, and any increase in well system pressure will reduce the effective capacity of the pressure tank (and should also be accompanied by adjusting the pressure in the pressure tank to a few PSI below the new low setpoint.) If your pump does not run at least a minute to refill the pressure tank (with nothing else drawing water) you should increase the size of the tank or add an additional tank.