Can you use the pilots for two Falcons interchangeably?

Yes. The model doesn't matter. All that matters is having the right pilot card and base token.

Yes, assuming I understand your question.

You can use either model of YT-1300 with either the Rebel Alliance or Resistance pilots. You would just need to make sure the pilot card and ship token match.

Edit: Even in a tournament this would be allowed since the rules say "They cannot modify a ship model in any way that would create confusion about which ship the model represents."

But in this case there could be no confusion.