How to change the graphics settings after the initial launch of the game

As far as I can tell there is no way to change the active character in co-op or single player mode.

The reason for this is that each character initiates a different perspective on the story. The first player's character is in charge of the story's events. Changing the character would compromise the background information and change a lot of the dialogue.

Short of starting a new game, I don't believe there is anything else you can do.

I had the same problem on Windows Vista 64-bit. After some Googling, I found nothing but I did notice that people with Windows XP did not have the same problem. Anyways, here's my solution:

For Windows Vista/7 users, you'll need to run the game in Windows XP Service Pack 2 emulation mode. Navigate to your Steam CoD installation: C:\\Steam\steamapps\common\call of duty Right-click on CoDSP.exe and click Properties In the Compatibility tab make sure the "Run this program in compatibility mode for:" is checked and change the drop-down to Windows XP (Service Pack 2) Hit Apply and the OK

After this, I was able to change the brightness from in-game without a problem. If this still won't help, try running it as an Administrator. You can follow the above steps but the checkbox is further down in the Compatibility tab.