..but last night I had an idea that is based on TheLiam's Overlay Window project (http://www.opserver.de/ubb7/ubbthreads.php?ubb=showgallery&Number=374348#Post374348).

What I think will work is this: I create two applications, one is the game menu and the other is the game levels. When selecting a new game or selecting the specific level from game menu I don't use level_load but exec to start overlay window (which will be all black). Overlay window will initiate the exe file of the second game-part but, because the overlay window will cover the startup screen of GS, the entire process will look the same as if the level_load was used.

Unfortunately I can't figure out the command that will start the game automatically because the code is in xml:( This is the original (TheLiam's) line of code:

<startbutton name="start" style="button_click" text="Spiel starten" file="Game\main.exe" x="16" y="16" width="75" height="24" backcolor="WhiteSmoke" forecolor="Maroon"/>

I've tried things like:
<open file="Game\main.exe"/>
<start file="Game\main.exe"/>
<startup file="Game\main.exe"/>
<main file="Game\main.exe"/>
..and few others but nothing worked, I was still forced to manually click on the button to start the game:(

Maybe you have some ideas on what to use in order for this to work?