How do I reassign the F3 key to another application?
Solution 1:
FunctionFlip allows you to change the function keys individually.
Solution 2:
KeyRemap4MacBook does allow changing individual media keys.
Save something like this as private.xml:
<?xml version="1.0"?>
<root>
<item>
<name>Change Expose to F19</name>
<identifier>B83A0F12-896A-42C4-AE87-1F24EE0B989E</identifier>
<autogen>--KeyToKey-- KeyCode::EXPOSE_ALL, KeyCode::F19</autogen>
</item>
</root>
Press the ReloadXML button and enable the remapping in the first tab.