After adding personal tags you may need to wait until the managed folder assistant processes the mailbox again before they'll show up. You can force it by runningStart-ManagedFolderAssistant <MailboxIdentity>.
As he tested on his Lab, and so did I, we used a retention policy with one folder having a RPT on it. With no personal tags the "Apply Policy" button is not in the Outlook ribbon or the right-click menu. After adding a personal tag to the retention policy and running Start-ManagedFolderAssistant the buttons and tag showed up after closing/opening Outlook.
> And from the Technet to complete :
Managed Folder Assistant
The Managed Folder Assistant, a mailbox assistant that runs on Mailbox servers, processes mailboxes that have a retention policy applied.
The Managed Folder Assistant applies the retention policy by inspecting items in the mailbox and determining whether they're subject to retention. It then stamps items subject to retention with the appropriate retention tags and takes the specified retention action on items past their retention age.
In Exchange 2010 SP1, the Managed Folder Assistant is a throttle-based assistant. Throttle-based assistants are always running and don't need to be scheduled. The system resources they can consume are throttled. You can configure the Managed Folder Assistant to process all mailboxes on a Mailbox server within a certain period (known as a work cycle). Additionally, at a specified interval (known as the work cycle checkpoint), the assistant refreshes the list of mailboxes to be processed. During the refresh, the assistant adds newly created or moved mailboxes to the queue. It also reprioritizes existing mailboxes that haven't been processed successfully due to failures and moves them higher in the queue so they can be processed during the same work cycle.
In Exchange 2010 RTM, the Managed Folder Assistant runs on a specified schedule. By default, it's scheduled to run daily from 01:00 through 09:00 (1:00 A.M. through 9:00 A.M.). You can schedule the assistant to run at a time when the Mailbox server is relatively idle or not under a heavy load. When determining a schedule for the assistant, consider other processes that compete for Mailbox server resources, such as offline defragmentation of the mailbox database and antivirus scans.
The Managed Folder Assistant doesn't take any action on messages that aren't subject to retention, specified by disabling the retention tag. You can also disable a retention tag to temporarily suspend items with that tag from being processed.