Using your retail key with the ISO's downloaded from Microsoft's "Evaluation Center" should be easy right? You paid for a license so you should be able to just activate a trial... Turns out it's not that simple. You actually need to change your server edition from ServerBlahEvalEdition to whatever edition you have a key for using
DISM /Online /Set-Edition:ServerDatacenter /ProductKey:<key for blah>
This command is going to yell at you for not accepting the EULA, so the final command looks like this:
DISM /Online /Set-Edition:ServerDatacenter /ProductKey:<key for blah> /AcceptEula
From what I gather the
Set-Edition option can be either of the following:
The command takes a good 10 minutes to run (looks like it stalls), then asks to reboot to cleanup. Afterwards, you should be activated and ready.