The F3 button on my rMBP has a figure which shows 3 rectangles, pressing the button without the FN key initiates the Expose function. I want to modify that key for another function. However I cannot directly modify it via preferences because pressing that button does not register as a specific keyboard shortcut.
You could also change it to a normal F-key with FunctionFlip.
If anyone else is looking for a way to change it with KeyRemap4MacBook, just create a private.xml like this: