There will be two scripts. One to allow users to add their mailbox to the container template group, and one to remove the group from their mailbox
The scripts will be run using an Execute Script step on an application rule. The scripts must be stored in a folder that is accessible to the Admin account.
enablefieldsubstitution
PUT PERMISSIONS DESKTOP #7012 Mailbox 19 0 "Custom Mailbox Toolbar"
Save the document
This script will replace #7012 with the user ID of the user initiating the script
enablefieldsubstitution
DELFLD PERMISSIONS DESKTOP #7012 Mailbox 19 0
Save the document
This script will remove the entry from the user's mailbox "Belongs to:" field