function menu_menu_link_alter(&$item, $menu) {
  $result = db_query("SELECT * FROM {menu_links} WHERE link_path = '%s' AND link_path = router_path AND customized = 1 AND module  = 'system'", $item['router_path']);

  if ($link = db_fetch_array($result)) {
    // Alter $item
  }
}