I know you can do this with AutoHotKey, a freeware program that lets you control Windows or basically anything; it has the simplest programming language I've ever seen (the only one I can write in so far) and it is freeware.
All AHK needs is a way to detect whether this emulator of yours is on or off; I have no idea how this emulator works, but with a bit of puzzling AHK will surely be able to detect it. Even if that were impossible, you could just have AHK use a switch that is toggled every time this shortcut is executed.
The AHK code might look like this:
~k::
;-----(here goes some line that detects the "state" of your emulator")
Msgbox, Emulator is now %state%.
return
If you press k (you can change it into any other key combination), AHK will look whether state is on or off, and display the state in a message box. Key press k is still sent to your emulator: AHK won't intercept it (though it could if you wanted it to).
You'd want it to display the state differently (not in a message box), of course, but this is just an example. I can't produce anything more specific without knowing how this emulator shows its state. If it is shown in a visible screen, AHK can very simply get the state by looking at the pixel colour.
