If Boba Fett is used to remove VI or Adaptability does the PS of the affected ship revert to its original number?
I believe the answer to be no it doesn't. Either upgrade card modifies to the new PS level at the beginning of the game during setup. There is no rule about changing PS during the middle of a game.
Also case in point. The Nashtah Pup is not allowed to have any upgrade cards equipped to it when it is deployed. However, if the Hound's Tooth were already equipped with either VI or Adaptability then the modified PS skill would apply when the pilot transferred over to the Pup.