Thanks. Actually VMware Support called me back today and gave me the instructions. They described mounting the writable template on a non AVM agent machine (similar to your advice), pull the 6 files off that can be used to upgrade the provisioned WVs.
Funny you say 2.12.1, since that's the problem we've been dealing with recently. The 2.12.1 agent caused massive problems with Office 2016 email attachments (MSI install on master image with KMS) and office doc downloads from the internet. They were being blocked. Somehow the agent was interfering with the Windows Attachment Manager and caused the OS to think they were unsafe. Log off and back on to a pool running 2.12.0 and everything worked fine. Totally weird and frustrating.
We ended up staying with 2.12.1 on the server, but reverted to 2.12.0 agent and WV with 4 exclusions added to the WV sysvol.cfg to fix the printers. All is working fine now, even with AppStacks. VMware claims to fully support this configuration, even on 7.1 (which is our next fun adventure).
Appreciate the reply Ray.
..mb