Upgrade PMG from v8 to v9 with minimal downtime.

[Lumir]

We want to minimize downtime by upgrade a single PMG. The PMG is VMware VM.
Can we use these sequences?

1. Stop PMG VM
2. Clone PMG VM to PMG VMCLONE (hostname persists)
3. Start PMG VM again
4. Start VMCLONE with different IP address
5. Upgrade VMCLONE by Debian and Proxmox repository. (PMG subscription is binded to hostname)
6. Shutdown the original VM
7. Change VMCLONE IP address to VM IP address
8. Restart the new VM
9. Delete the original VM
   
   I understand there will be a gap in mail history but no matter.
   The crucial question is whether two machines with the same hostname and the same subscription can be supported.