It would be nice if the !permission command took human readable/user-friendly input.
!permission username moderator
!permission username 2
Since memorizing what number is associated with what role is not something you can really expect every administrator to do.
You could have multiple options for each permission level, for example: 2, mod, moderator
This way you continue to support the current methodology, but allow for more user-friendly input that accounts for alternate phrasing.