Requesting for Fullscreen mode

I want to compress and play my game in automatic Fullscreen mode.

I've searched and used many kind of script but those scripts are not the ones I would like to use.
Some were prompted me if I will play in fullscreen or windowed. Some scripts just added an option in in-game menu to select

if you want fullscreen or windowed.

I even tried using the "GAME>LAUNCH IN FULLSCREEN" option, but it only works in test game, not in a compressed game.

I want a script that when I start my game, it will play in fullscreen mode already but still has an option to return it back to window mode

when already playing the game.

Reason: (how do I explain this in english, darn)
I had this game intro that I need to sync the background music to the scene. In window mode, if the scene started showing, then I click my mouse outside the game window (eg: I clicked on my desktop), the music will play continuously but the scene get paused. As a result, the scene will bypass the music that supposed to be in extreme part of the music.

Or maybe, a script that will pause everything (runnning scene and BGM) if I click outside the game window.

Sorry for my grammar and for being a ignorant in scripting. Thanks!