Ok, nerd rage time. There's always been that moment of Executive Meddling [http://tvtropes.org/pmwiki/pmwiki.php/Main/ExecutiveMeddling] that shreds a beloved franchise like the guy's head off of Scanners.
Examples: Gordon Freeman speaks for the first time, and it's "Oh. My. God. I just totally whacked those bozos.", Highlander 2, GTA V being set in Rapture (ooh, two in one shot), Someone writes a Twilight mod for Castlevania...
Nows your turn to play:
What's the one way you would use to destroy an entire franchise, that hasn't been done all ready?