How can I change graphical settings without launching the game?

I am encountering a persistent DirectX error that began after beating the boss of the prologue, and has since prevented me from from even launching the game. The most likely cause that I can figure after some Googling is that I set one or more graphical settings beyond the capabilities of my system.

However I am having difficulty troubleshooting this point, as I cannot figure out how to alter the game's graphical settings from outside the game. I cannot even reach the menu screen without the above error crashing the game before it loads to that point.

So is there any way to alter the graphics settings from outside the game, or is my only option to reinstall the entire thing from scratch?