You can revert your settings back to normal by opening the folder you installed the game to:
(usually C:\Program Files (x86)\Renegade X) and looking for "..\UDKGame\Config\UDKSystemSettings.ini". Delete that file and boot the game up and the settings will be back to normal.
After you reset them, you can tweak the files again to see just what makes it crash.
ALTERNATIVELY, you can launch the game, let it crash, then post your log file. There is a stickied topic on the tech support forum about how to retrieve your launch.log file.