I have never done this mod, but it is included in the “Big Steaming Pile O’ Mods” for fuzz face type circuits. These mods can be found on the http://guitarpedalbuilders.blogspot.com webpage. This is a very easy mod as all one has to do is place a B100K pot between the 9V power supply and the 9V power eyelet on the PCB. If using a BYOC 3PDT board, the mod would appear as in the below drawing. The 100K pot value allows one to take the voltage down to zero if so desired.
