There are significant changes, so starting over will most likely be required. You *might* be able to continue a save if you don't care about new things, but it will probably break. You have at least a few weeks before it is out on console to finish up a current game, and you can always choose not to update until your current game is done. And don't forget that this game is intended to be played over and over in new games, so starting over really isn't that bad unless you are in the middle of a big build or something.