It's possibilities like this that should make the world think twice about putting all their eggs in the GPS basket. The US military has always said that while it doesn't mind the rest of the world using its system, it retains the authority to do what it wants with it.
Unless and until we transfer control of GPS to a civilian department, we should think twice about retiring all the ILS, VOR, and NDB navaids, like they're currently planning.
I wonder if LAAS and WAAS would be affected if the SA is turned back on?