Hempy,
I do not profess to k now the technicalities, either for how you can limit access to either GBAS (LAAS) signals or the precision Galileo signals, only that it can be done.
A significant factor in financing Galileo apparently revolves around this feature, and much $$$$ argument amongst European governments about what happens if the revenue is not up to expectations --- this is part of the reason for the long delays in getting Galileo satellites up.
I am not certain even whether the arguments about which signals will be freely available, or whether all will be available free is yet settled. Galileo is way behind schedule.
At least third Generation GPS only involves the politics of one single government.
Tootle pip!!