How to override the back button of the device and not just disable it.

I have this code to disable the back btn

     public override bool OnKeyDown(Keycode keyCode, KeyEvent e)
        {
            switch (keyCode)
            {
                case Keycode.Back:
                return false;
            }
            return base.OnKeyDown(keyCode, e);
        }       

Is it possible for me to write what i want it to do?