You forgot the most important in case of Uninstalling...
HTML Code:
<uninstallcode><![CDATA[$db->query_write("ALTER TABLE " . TABLE_PREFIX . "usergroup DROP skhardmodpermissions");]]></uninstallcode>
Just in case someone has uninstalled your hack and is trying after to reinstall what results in getting the dreaded DB Error. Just a side note

Great hack and good idea by the way -
Installed 
Thank you!