Disable Screen Mirroring Keystroke
There doesn't seem to be an entry for the shortcut in com.apple.symbolichotkeys.plist. The media keys cannot be configured in DefaultKeyBinding.dict or keylayout files. I didn't find any hidden preferences with strings either.

I was able to disable it with KeyRemap4MacBook, but only on my laptop's keyboard; not on an Apple Wireless Keyboard.


Save a file like this as ~/Library/Application Support/KeyRemap4MacBook/private.xml

&lt;?xml version="1.0"?&gt;
&lt;root&gt;
  &lt;item&gt;
    &lt;name&gt;Disable Command-F1&lt;/name&gt;
    &lt;identifier&gt;private.disable.command.f1&lt;/identifier&gt;
    &lt;autogen&gt;--ConsumerToConsumer-- ConsumerKeyCode::BRIGHTNESS_DOWN, ModifierFlag::COMMAND_L, ConsumerKeyCode::BRIGHTNESS_DOWN&lt;/autogen&gt;
    &lt;autogen&gt;--ConsumerToConsumer-- ConsumerKeyCode::BRIGHTNESS_DOWN, ModifierFlag::COMMAND_R, ConsumerKeyCode::BRIGHTNESS_DOWN&lt;/autogen&gt;
  &lt;/item&gt;
&lt;/root&gt;

Press the ReloadXML button and enable the new remapping in the first tab