I've about given up on my previous problem. I was beginning to think it'll be easier to do simply by dropping the user, then recreating it with the appropriate privileges next time around. Only, when I tried (as the superuser, no less) to drop the problem user, I got the following:
mysql> drop user 'dtuser'@'10.%'; ERROR 1268 (HY000): Can't drop one or more of the requested users
Anyone have any clue a)what the error means beyond the obvious, and b) why I wasn't allowed to drop the user?
Edit: I did make a couple of changes to a set of user lines in mysql.user [Update_priv] and [Alter_priv], but I then changed them back to what they were before. Could this have anything to do with the reason I cannot delete the dtuser user?