Panel>Kategoriler>Veri sekmesinde Sıralama alanını kullanarak yaparsınız.

Bunun için değişkeni değiştirin;

$category_products = $this->db->query(
            "SELECT cd.name as category_name, ptc.product_id
        FROM
        ".DB_PREFIX."product_to_category ptc LEFT JOIN
        ".DB_PREFIX."product p ON (ptc.product_id = p.product_id)
        LEFT JOIN ".DB_PREFIX."category c ON (c.category_id=cd.category_id)
        LEFT JOIN ".DB_PREFIX."category_description cd ON (ptc.category_id = cd.category_id) 
        WHERE
        ptc.category_id IN(".implode(',',$category_list).")  AND
        p.status = 1 AND
        cd.language_id = '".(int)$this->config->get('config_language_id')."'
        GROUP BY ptc.product_id ORDER BY c.sort_order ASC ")->rows;