Edit: Found a solution by using the D3D9 update.

**NOTICE**

Using this update I am able to adjust brightness/resolution in game while still in D3D mode without needing to use the D3D10 renderer! Kentie's launcher is still required to enable this.

http://www.cwdohnal.com/utglr/ -- "Direct3D9 renderer version 1.3 for Deus Ex: dxd3d9r13.zip (107 KB)."

Hmm, where do you put the .dll?

I put everything in the 'System' folder, after doing so D3D9 became an option in the Kentie launcher. It's worth noting though that by using that .dll file mirrors no longer work in game for some reason.

Glad this was able to help someone else. I went ahead and marked your post as the solution to this thread so others won't think it's still open for help.