$sourcedir/Memberlist.php
Pesquisar
$_REQUEST['sort'] = 'realName';
Alterar
$_REQUEST['sort'] = 'registered';
Pesquisar
$context['sort_direction'] = !isset($_REQUEST['desc']) ? 'down' : 'up';
Adicionar e trocar por
$context['sort_direction'] = !isset($_REQUEST['desc']) ? 'up' : 'down';