I’ve not tried it but assuming that you are talking about the Two Stroke circuit, although it is true that a master volume control would reduce the signal strength from the preamp tube to the power section, the decrease in picking dynamics (one of the best features of the Two Stroke design) would probably suffer significantly. Also, the quality of any distortion increase would probably be of rather low quality. Remember the Two Stroke is a single-ended class A design and as such, does not have a phase inverter, where a master volume control would normally be installed for best tone performance. The Two Stoke is not a “hi gain” amp so even though it breaks up nicely at full power it will never sound like a Mesa Triple Rectifier (or other hi gain design).

That said, a master volume control is a simple circuit and would be easy to fit if you wanted to try it.