I see this as a chance to fix great lost opportunities of the past:
Arsenic and Old Lace
(1944) should have featured Boris Karloff, not Raymond Massey playing a Karloff lookalike. (Backstory: Karloff was too busy playing the part on stage to do the movie version, even though the whole joke is that the character is a dead-ringer for Karloff.)
(1966) should've featured Julie Newmar as Catwoman, not Lee Meriwether. (Newmar was busy shooting another movie at time.) Even as a kid, it bugged me that the movie didn't have the "real" Catwoman . . . .
West Side Story
(1961) should've featured Elvis as Tony, who would have been a lot more memorable than whoever it was who actually played the part (whose name I can't be bothered to look up).
Oh, one more: Let's put Sean Connery in On Her Majesty's Secret Service
instead of Lazenby, just because it's a crying shame that we never got Connery and Diana Rigg together in a Bond movie!