If you’ve had the pleasure of rolling out KMS hosts in an environment where, previously they had been using MAK keys, you’ll notice that if you re-arm KMS clients they will insist on rebooting for the changes to come into effect. Not ideal!
The easiest way I found around this, was to use the provided keys from the Volume Activation Deployment Guide Windows 7. Shown below is the key for 2008 R2 Standard.
Windows Server 2008 R2 Standard Product Key — YC6KT-GKW9T-YTKYR-T4X34-R7VHC
First reset the license key with ‘slmgr -ipk ProductKey’, then force the machine to activate with ‘slmgr -ato’.
Sorted! Reboot avoided.