Originally Posted by
Heathrow Tower
No, this would only affect the callsign, not the flight number. Many flights already have different callsign/flt no. pairings for this reason. i.e. BAW939 = BA939, but BAW27G = BA727.
Is that the same everywhere in the world, though? ISTR that the BA25/BA26 pair (HKG) was renumbered to BA31/BA32 because of the possibility of callsign/flight number confusion over China, which IIRC does not permit callsigns that are not aligned with flight numbers.