I tried editing the file, but when I try to save it I get, "access denied."
I also tried unsuccessfully to set NOSOUND=TRUE in DOSbox, but that also didn't work.
My only DOSBOX game right now is TES Arena, so I played around with it. Here's what I did to get sound to mute (I think it's a bit unconventional).
Normally, what I need for a batch file was:
dosbox -noconsole -fullscreen -c "mount c 'e:\ELDERS~1\ARENA\ARENA\'" -c c: -c arena
I made my own batch file called NOSOUND.BAT with the text:
MIXER MASTER 0
MIXER SPKR 0
MIXER SB 0
MIXER FM 0
I put the batch file in the arena directory
And then when dosbox started up, it muted everything. Then I just typed "ARENA" to run Arena.
I hope that helps you adapt it to MIght and Magic.