Why do you need it? Changing those values can lead to performance drop since SQL server can index 450 character only. So, the size is set to cover 9 levels in the tree. I would rather recommend using separate fields in the page type. One for the short name - and this one will be used as the page alias source. And second field, where the editor can add the full value. Then, in the front end code get the first one for the URL and second one's value for the content.