Manual backup is the only way I know.

I would think even if you do a backup of both prior to your vendor doing whatever he's doing, restoring the backup might undo something that he's done. Depending on what he's doing, he should do a backup of the system if needed. The VM is your responsibility for backing up normally.

I suggest when the vendor is in, test it all before he leaves.

Scientists say that the universe is made up of Protons, Neutron & Electrons. They forgot "Morons".
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