It's a new feature we just added that I haven't find the time to put in the manual yet. The new hotkey it's shortcut to access GSX directly without passing through the YouControl menu on a scenery (typically FSDT sceneries) that has its own YouControl menu.
Before this addition, if you were on an FSDT airport and pressed CTRL+F12, you first had to go through an intermediate menu that asked if you wanted GSX OR that airport YouControl menu (that controls special scenery features, like opening hangars, special jetways, etc.).
Now, if you use the alternative hotkey CTRL+Shift+F12, you'll go straight in GSX without passing through the YouControl choice menu, saving one menu step.
It might be a useful feature for users with programmable joysticks/keypad (or even speech control) that can create macros to control GSX almost hands-free, without having to worry if the airport has a YouControl menu or not, which will screw up their macros.
