If you’re doing this via messages (not category permissions) you don’t need to worry about that. Have your “staff” group (keep in mind staff is a built-in group that is all admins plus all moderators, so you’ll need a different name) created, then send a message to “staff” + username. No need to modify groups each time to add one extra person, simply add them to the message.
Edit: ninja’d by @fefrei 