That's all you would need to do. You could also edit: /upload/include/client/open.inc.php
and add the asterisk ( * ) so users know you have to have that.
For number length you would edit:
File: /upload/include/class.validator.php
Line: 133
Find:
return (!is_numeric($stripped) || ((strlen($stripped)<7) || (strlen($stripped)>13)))?false;
And change to: (As an example of 10)
return (!is_numeric($stripped) || ((strlen($stripped)<10) || (strlen($stripped)>13)))?false;