Katie Holmes As Rachel Dawes In "The Dark Knight" Trilogy, Replaced By Maggie Gyllenhaal
Christopher Nolan wanted Katie Holmes to portray Rachel Dawes for both Batman movies, but because of scheduling and personal problems, she had to refuse it. Maggie Gyllenhaal replaced Holmes and acted in one of the best Batman movies ever. The good thing is that there are no hard feelings on all sides.
Also, how would anyone be able to tell when some background character in GoT was replaced? There were a ton of them, and they all looked the same.