Now we know why I no longer support bare-metal installs a. k. a. non-virtualized environments.
In the situation of doing the mass mapping, I would just take a snapshot of the virtual machine, try the mass mapping, and revert back if it didn't work. Same with the upgrade. Saving a snapshot takes seconds. Reverting to a snapshot takes minutes.
For you bare-metal install guys, if something goes wrong you get to spend 1.5 days restoring from backup. Maybe more.