So... @noxx kindly gave me a script that allows me to press "start and select" on xbox controller to exit whatever emulator and return to bigbox. With this starting point iv learnt how to "select + lb" = save state and "select + rb" = load state. Feeling confident I decided I was going to BADLY write a script that when in bigbox mode pressing "select + start + lb + rb" would run a fullscreen png saying "shutdown pc, a = yes, b =no" etc. Pressing "a" will shutdown pc, pressing "b" would kill png and return to bigbox.
And then it occurred to me after 2 days of writing this that bigbox will have a shutdown option wont it. Of course it ******** does. What a idiot. lol.
Im working towards a controller only machine, no keyboard or mouse, I have nieces and nephews that break stuff so my suggestion/request is to allow "shutdown" while locked for bigbox. Please. Much the same way as "allow exit while locked".