Are there not laws regarding the use of false markings on military aircraft in international or foreign airspace? In any event I would expect the RAF and MAA to throw a fit over any such subterfuge.
I would also speculate that the whole idea of performing public displays in the UK with an aircraft currently grounded by MAA would raise the odd eyebrow in Whitehall and the legal profession.
Alternatively, this may be an attempt to blame the uptight, panty-waist Brits for a no-show and deflect attention from the fact that the US-made engine done blowed up for reasons (as yet) unknown. I'll go with that one.