When I was flying both civvie(private) and military quite a lot and using separate Nomex suits for the two, I went and asked our flying clothing servicers that question. They assured me that the RAF suits simply went through a washing machine on a low temperature cycle and got no special treatment.
I really can't believe that the best air force in the world, where even the procedures for cleaning the floors go through formal assessment and approval would be missing a trick there and if some reproofing was needed, it would have been done.
G