Currently, the AbuseFilter warnings are all in the MediaWiki: namespace. As a result, they can only be edited by users with the "editinterface" right. However, on some wikis (such as English Wikipedia), the "abusefilter-modify" right is given to non-admins (in the case of English Wikipedia, it's not even part of the admin package). These messages should be considered an extension of the filters, and not part of the interface. Probably, the easiest implementation would be to create a new namespace for these.