I am tryng to do the same thing. I’m using an expression pedal to go between the 3rd and 4th harmony. The struggle is to get the bypass on and off quickly when you go back to the verse. If you miss Bypass the first chord back sounds ugly. Trying to figure a way out to have the pedal on 0 be bypass and then when I go above 1/2 its the 4th and 100 the 3rd. Have not been able to get that going yet. This way your foot is always on the expression and not jumping from bypass to expression and vice versa. Any ideas on this would be greatly appreciated.