Game Crashes on Launch

I'm using the Steam Version of the game, and all the DLC's to date, and I know the game runs on my computer because I pre-ordered the game in August and have played it a lot since. Recently I changed a video setting, I think Anti-Aliasing to 4x, just to see, because before I've had it on 2x, and I've been fine at 30 fps, but when I did this, every time I launch the game, it will launch through Steam, the window will not even open before it says I'm not in a game anymore, implying it tried to run but then crashed, because of the changed setting. Any advice as to how I would be able to change the video setting without actually launching the game, maybe a Steam Set Launch Option or something?