Would you like to switch different tone-caps by foot or what is it you plan to switch? For switching different cap-values by foot you could install one permanent capacitor and add different parallel or series capacitors by switching 2 relays. The relays could be powered off the (rectified) heater supply, but be careful not to mess up your heater-balance.
If that's what you aim for I think it's a bit too much for this kind of amp. Of course it would be doable but I think the cool thing about the amp concept is the simplicity. I didn't play it myself yet but I think it's thought to deliver one sound really well rather than offering many different compromised sounds.
However, if you really want to mod it I'll be happy to help if I can.
Have fun!
