Official patches are here, scroll down for earlier patches.
You can downgrade from v1.0.4.0 to v1.0.3.0, but you cannot downgrade to v1.0.2.0 from a later patch except that you can reinstall and repatch.
On the other hand, I'm not absolutely sure that's what you are asking for. What is a graphics downgrade?
It's a patch that downgrades the graphics for under requirement computers. I have all the requirements except my video card witch is a ATI readon x1650 pro and the requirements is a x1900
Or, you could, ya know, buy a better computer. If you know your computer doesn't meet the requirements, why are you trying to run the game? Unless you have a laptop, you can easily pay like $100 and get an actually pretty decent card.