Instead of using the wrong equipment identifier, you could always ask the briefer if there is anything affecting GPS in the route of flight.
Of course, in this case, that there were massive GPS anomalies predicted was published in all sorts of aviation publications, including AOPA, Avweb, Flight Aware, etc. It's a great reason not to rely on GPS as the only means of navigation. While Selective Availability hasn't been employed in several years, the fact is that the GPS system is still operated by the Air Force and can be shut down or modified in seconds for "military necessity", testing, or whatever reason seems good at the time.
Not the best idea to file with an improper equipment identifier. Using an equipment identifier implies the ability to actually use the equipment. Note the /G caveat: "Global Navigation Satellite System (GNSS), including GPS or Wide Area Augmentation System (WAAS), with en route and terminal capability
." That's why having a handheld GPS isn't /G--none of them have terminal capability--even in VFR conditions on a VFR flight plan.