actually there is a module, i'm testing it but i cann't get it to work, you can use position to add levels and it has the posibility to choose between all users and members only
if you are interested here is the link to download it.
https://xoops.org/modules/repository/singlefile.php?cid=62&lid=1137
i posted at
https://xoops.org/modules/newbb/viewtopic.php?topic_id=35066&forum=28&post_id=152098#forumpost152098
why it didn't work for me
tell me if you can get it working
raqxx