I never use published settings if I can help it. Making a new one is half the fun for a DM. But for something like a Star Wars RPG or the Dresden Files RPG, I just claim Alternate Universe. Everything's the same except when it isn't.

Case in point: I want to run a Homebrewed Star Wars RPG later this year. I dislike much of the Prequels and I don't want the players to run amok in the middle of the movies because they will immediately try to screw with stuff (kill Vader, steal the Millennium Falcon, punch Yoda in the face, etc), and that breaks immersion. So, I just assume the campaign starts sometime after the Force Unleashed 1 Darkside Ending. That ending (and the extra missions it unlocks) changes so many things about the setting that the players don't feel like following the movies or deliberately breaking from the movies, since now nothing is the same, and yet it's still very familiar.