Hi Rockster,
You could try setting the Advanced Launch option under each game properties..
After you set the launch option, run the game and it will permanently change the dxlevel in use...delete the launch option if you want to save the new video settings after the first run and if you want to use dx9 again just change it to -dxlevel 91 and follow the same procedure..
There are heaps of other options to try...from scripts to hidden Steam functions it just depends on what you want to know...
Steven