Even though I don't particularly care for push pull pots and little switches all over the place, I have modified some guitars that had this capacity by switching out caps on tone pots and resistors on volume pots. For example, a 1 Meg pot switched to parallel a 500K resistor, you end up with a tapped 500K control. I have also made taps on pots that would allow normal control until around 8, then boost the signal with a pot turn to 10. Just a little louder but enough to cause some overdrive, then back off to 8 for standard loudness. You can use a switch but, I've trained my pinkie finger to roll the volume pots.
Steven