QUOTE: "8. Yanks go to war and decide to turn the civi off."
Can't actually be done easily. What we use is actually the Coarse Acquisition signal, which is needed for the secure military precise system to get a fix relatively quickly (i.e. better than a few tens of hours). The net result is that although Selective Availability (SA) jitter can be turned back on at will, or indeed changed from the default 100nS randomisation to another value, it is extremely unlikely that we will completely lose the signal.
Jamming is dead easy though, particularly over short ranges, as the sub-noise floor, spread spectrum, technique used for GPS makes it very susceptible to blocking by even modest jammer power levels.