newbie error

Please correct me if I'm wrong but to customise the template I needed to copy it to my theme folder and then include the following in my template.php:

function <themename>_theme() {

  return array(
    'admin_message_message' => array(
    'arguments' => array('node' => NULL),
    'template' => '<pathtotemplate>admin-message-node',
    ),
  );
}

Hope this helps someone and if I'm right it might be worth adding to the already helpful documentation,
Crom