You can add a PRV (pressure relief valve), or adjust the one that is already in your system.
That will reduce the max pressure to all implements though.
I did the opposite and increased my PRV around 20%.
What would happen; if the difference is small, 25%, nothing will happen. 25-50% probably nothing will happen but you never know, 50-100% over pressure, then you're really pushing your luck.
What would fail first is really down to the engineering of the thing. Generally, the safety factor of the mechanical parts should be at least 5, so the weak point is the hydraulic motor. Most likely the seal would fail first.
I have a hydraulic motor on my hedgecutter rated at 150 bar (2200psi); I have the PRV set at 225 (3250psi) and so far it's doing just fine.
Note that normal running pressure is only around 60 bar (900 psi), it only goes high briefly when it hits something tough, or stalls.
I recommend the installation of a pressure gauge. I don't know why they aren't standard.