Scene Graph back button

Right now, the back button is exiting me out of my application. I'm displaying a modal by changing opacity on 2 groups but I want to use the back button to close it. It doesn't actually change the screen.. it just modifies the state. Can I catch the back button so it doesn't exit me out of the view? This is a pretty principal part of my application that I'm hoping won't be limited by auto functioning back button.

Or it's possible I have some legacy code in here. 

So question is: Can I catch the back button for Scene Graph without it exiting my current screen?

Thanks!