Trudy Cooper is shown complaining that Jim Lovell gets Apollo 13 because he was Alan Shepard's backup, this Gordo screwed himself, but it was a complete crew swap. 13 for 14. Gene Cernan was Shepard's backup, if Shepard couldn't make his moon flight, Cernan would have gone in his place...
shareYeah, that's mentioned in another thread.
FWIW, on the show (and in real life) the 13/14 crew swap didn't have that much to do with Cooper being bumped off. If the characters had described the swap correctly in that one little scene (Lovell went from commander of 14 to commander of 13, not from backup to prime), it wouldn't really have affected the narrative in any other way.