their is no reason you cant do whatever you
want to in your own home...
if you dont like it at 80 psi, cause you like to be
sandblasted by multiple shower heads in your shower
that is your choice..
things will simply last longer if you kick it
down to 60--70 psi.....
ballcocks, washing machine hoses and water heaters
simply live longer with the lower water pressure..
if you are going to leave it at 120.
I suggest that you be sure that your washing machine hoses are braided SS ones.
eventually the expansion tank on your heater will blow a gasket seal inside ...
I hope that your pop off valve is going to a good floor drain for the
day it finally blasts loose...probably at night this will happen.....
so just be sure to pipe that line somewhere