Apple - Configuring custom keys on bluetooth keyboard

Download and install KeyRemap4MacBook.

Open EventViewer:

open /Applications/KeyRemap4MacBook.app/Contents/Applications/EventViewer.app

Press the key that you wish to customise and note the KeyCode:::

Create a private.xml like this:

<?xml version="1.0"?>
<root>
  <item>
    <name>Modifier Remapping</name>
    <identifier>modremap</identifier>
    <autogen>__KeyToKey__ KeyCode::CONTROL_L, KeyCode::COMMAND_L</autogen>
  </item>
</root>

Replace KeyCode::CONTROL_L with the key that you wish to change and KeyCode::COMMAND_L with the key that you wish to replace it with.