if you did it with a DMM i wouldnt think so. because you set it the estimated "max rms" output. but if you set it by ear, iwould go buy a cheap multi meter and set it that way
If it was set correctly to begin with, it will not change. The gain is set based on the output of your receiver, it has nothing to do with the box, unless you are overpowering your subs and need to dial it back a bit.