I don't know why you would need to change that, which is how is supposed to be and, in fact, it's a feature of the full support we have for PMDG.
Since GSX cannot even start on a parking spot if you are not with parking brakes set, by recognizing wheel chocks as an alternate way of keeping the airplane braked, GSX is not forcing you to always keep the parking brakes even after chocks has been set, which is what would happen if GSX only wanted parking brakes.
