How do I change the default function key functions?

[KelchM]

Is there any way to change the functions tied to the function keys Note: I mean the function keys, not the generic f keys. (I'm talking about brightness, volume, etc) I want to retain the ability to use my F keys by hitting the fn button.

 

[TheReef]

I'm not sure about changing the existing functions of brightness, exposé, dashboard etc. But you can add some functions to the other keys, eg I am now using exposé with F13, F14 and F15. (which you set in System Preferences).

I know that still won't change the existing keys though. (F4 is all windows exposé as well)