However, I would like to be able to remove members from this group in the future if they aren't as active, reverting them back to standard privileges. This would mean that they would no longer be able to have a custom title.
I've tested this and when a user is removed from the group, they can no longer change their custom title as the field is no longer visible to them in their personal details. However, the custom title still appears in their posts.
Is there a way to automatically revert the user's title back to the 'standard' ones I'm using for the rest of the members on the forums? I'd rather not have to manually delete their titles in order to do this.