MainStage: changing expression pedal control based on button state

Awesome! Thanks so much for the quick reply. Yeah, I kinda ended up with a simplistic version of what you describe. Basically, it was one Scripter on the instrument's channel strip that goes like this:

buttonPressed = false
function HandleMIDI(event)
{
	if(event.number === 21 && event.value === 127){
		buttonPressed = true
	} else if (event.number === 21 && event.value === 0){
		buttonPressed = false
	} else if (event.number === 11 && buttonPressed === true) {
		var newEvent = new ControlChange
        newEvent.channel = event.channel
        newEvent.number = 10
        newEvent.value = event.value
        newEvent.send()
        return
	} else if (event.number === 11 && buttonPressed === false) {
		var newEvent = new ControlChange
        newEvent.channel = event.channel
        newEvent.number = 1
        newEvent.value = event.value
        newEvent.send()
        return
	} else {
		event.send()
	}
}

It works okay, although it's a bit slow. That might just be JavaScript being JavaScript, though. I was hoping there was a way to do it without scripting, but maybe not. ChatGPT said there was something called Modifiers, but I don't think that's a real thing as far as I can tell.

Anyway, the end goal is that I have this AirTurn BT500S-6 Analog Controller and an expression pedal. I was hoping to get it so that the expression pedal would affect a different aspect of MainStage (Modulation, Volume, Pan, Expression, etc) depending on what foot switch I'd recently pressed. Right now I'm just mocking that up in the Workspace. Like I said the script works, but it'd be cool if there was a way to do that without having to write custom JS. It feels like the kind of thing that would be supported, but I'm still pretty new to this, so I could be wrong. Thanks again!

Follow-up question: I have a modifier set up in an instrument's channel strip that re-assigns Expression to Mod Wheel. I have a button set up in Workspace that adjusts the modifier's bypass so when the button is inactive, the modifier is bypassed. When the button is active, so is the modifier. Just like you described.

Now I'm thinking about having four modifiers total that do the following:

- re-assign expression to mod wheel

- re-assign expression to pitch bend

- re-assign expression to volume

- re-assign expression to breath

How do I add a second button so that:

- When neither button is active, the first modifier is active

- When only the first button is active, the second modifier is active

- When only the second button is active, the third modifier is active

- When both buttons are active, the fourth modifier is active

If you know how binary works, the buttons act like 00 = modifier 0, 01 = modifier 1, 10 = modifier 2, 11 = modifier 3

Ah, perfect! The modifier + button hooked up to its bypass is exactly what I was looking for. Much better than the scripter. Thanks so much!

yeah, that's what I was thinking too. Okay, great to know nonetheless. Thanks!