Is it possible to make shift X work while inverted? Or make a different command to fly inverted without having hands on?

As far as I know, all the "piston" slapper engines of WW2 had "float" type carburetors, which when turned upside down, as in inverted flight, the actual float device would shut off the fuel supply and the engine would shut down.
As engines improved and pressurized carbs became the norm and when direct fuel injection was introduced, then the engine would run upside down as good as right side up! And before anyone comments on it, "turbo" charging, or super charging has nothing to do with introducing fuel into the cylinders, all the "blower" does is keep a constant 14.7 lbs per square inch in the upper deck of the carburetor! As newer and improved "blowers" evolved, and manifold systems were improved, which then could keep the fuel pressure constant all the way to the intake valve! but that is a whole different topic!