Yes
You obviously *can* have your own menu in a WAF app (check the browser's implementation for details), but this won't allow you to gain more privileges. You won't be able to run commands etc.
This makes sense, because otherwise, that would essentially mean giving full root control to a WAF application, which would be a gaping security hole.
The only way that I *think* you can interact with the system is via LIPC. I haven't taken a deeper look into this, but do some "grep -ir lipc" inside the WAF and pillow directories and see how it's used. Good luck
PS: There is no exit button. The exit button is the home button. This is true even for the bundled WAF apps (e.g., browser): If you start the browser, you can only exit it by returning to the home screen. If you look at the list of running applications, you will see that the browser is still running in the background after you "exited". I think it will only be killed once another WAF app is started.