Wow! Nice hacking! 
It does seem unfortunate that some group settings are not available for the automated groups like trust levels. It should be possible to set the user title based on the trust level group they are in but it is not.
You could try doing this using the badge system. Create a badge that is granted when a member reaches the trust level you want, and then set the “Allow badge to be used as a title”.
You can then create an automation using the “User group membership through badge” script that runs every day and updates the user’s title and flair.
