I would like to be able to hit a foot switch to change the parameters of an already active effect. For example, changing the EQ for piano leads. In the case of a piano part (or any part) currently utilizing both effect A and B in a performance, is there a way to set it up so that when I hit a foot switch it will boost/change existing active effect parameters, and when I hit it again it returns to its original state? Or is this a case where I might have to stack performances back to back, or a case where I would need to have one of the effects turned off in the saved performance and utilize it specifically for this purpose?
A Foot Switch, which can send either 0 or 127, is never going to be enough of a controller to adjust an EQ.
You can use a Foot Switch to advance to the next Performance, this will accomplish your goal.