Check out the image above.
It shows how to wire a potentiometer that can control the volume on your output signal. A pretty simple mod that could be quite handy! An audio tapered 100k (A100k) Pot would work nicely for volume control. The image below points out the pin numbers on the potentiometer.
Will this work as a purely passive way to control volume if, for example, I wired it as shown to two 1/4″ jacks as an in-line level limiter?
Yes Rob, this will work passively
Thanks! I was a bit worried about noise being a problem like it can be with passive mixing.