Recently I input the wrong key for my Office 2016 installation so I needed to change it.  I couldnt believe it when the documentation said uninstall and reinstall it so I decided to dig deeper.  Anyway, to cut a long story short just run the following command:

cscript “C:\Program Files (x86)\Microsoft Office\Office16\ospp.vbs” /inpkey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX