Once you change the master EQ settings, they will remain in place until you either reset the OS or change them again. No need to store them.
The only reason the volume would change between registrations is that the volume was changed when the registration was made.
Hope this helps,
PSR-S950, Bose L1 Compact, TC Helicon Harmony-M, Digitech VR (2), Crown CM311A, Samson Q7, Sennheiser E855, Custom Console, Morgan 33 Out Island Sailboat, and lots of other silly stuff!