Can I install a new pressure-reducing valve inline with another one?
Yes you can add additional PRV or regulators. The only possible side affect is a reduction in flow as they usually have restrictions. I have machines that I use 2 regulators one to do some basic isolation from the heavily fluctuating main air down to a fairly clean 90 psi then a second to provide a rock solid 80psi. And this machine runs great with no mishandling like that so Yes get the pressure down to what you want.