In /osticket/upload/include/staff/header.inc.php you should find lists with the id of main_nav and sub_nav, which include the array names for the tabs and submenu items.
You can change the submenu labels for the staff control panel in /osticket/upload/scp/tickets.php:
$nav->addSubMenu(array('desc'=>'<STRONG><s>**</s>Closed Tickets<e>**</e></STRONG>', ...
I can't dig much further at this moment, but I hope this at least helps a little?