It used to be more common, perhaps, for a tentpole to have its score replaced. I read somewhere that this was commonly the first step in major post-production revisions. See also: The 13th Warrior, Troy, Timeline, and even 2001: A Space Odyssey. There is also Ridley's own Legend and, to a lesser extent, Alien and Prometheus, to consider. All of these were re-jiggered not because of the schedule, but because either the studio or Ridley didn't like the score.