You are better off leaving the receiver at 100 watts and just not turn up the volume so high. Underpowered amplifiers cause more speaker damage than and overpowered receiver. I am not much of a tweaker whether it is computer equipment or audio equipment.
The registers are just an internal control. Kinda like a
master volume control. Adjusting them should be
But like anything else, don't proceed unless you know what
you are doing, or have a girlfriend with a degree in media arts,
or have an electronics tech store down the street with the info.