Had Windows not been this tolerant, I would have used Microsoft’s VAMT tool to manage keys. This tool lets you manage activation for a fleet of machines all at once over the network. Most importantly, it can operate in “proxy activation” mode, in which it talks to Microsoft’s activation servers on the machines’ behalf. When it does so, it captures the resulting activation certificates. You can save these certificates to a file and re-apply them later, whenever the machines are wiped.
Now that I know about VAMT, I intend to use it for all future Windows activations on any machine. Being able to back up the certificate and re-apply it later is much nicer than having to call Microsoft and explain myself whenever I re-install Windows.