I have not been able to find any specific documentation about Office activation (much like Windows) but what I have found shows that the same rules seem to apply - if the application is already activated it should stay that way. it will discover KMS via DNS, and when it comes to validate activation with the new KMS server should behave the same way as Windows.
I would recommend the same as above, using VAMT to force the first 25 machines to re-activate with the new KMS server to get above the threshold.
Just setup the Windows KMS server and in no time the KMS count got to 16, i am just going to leave it a while it should sort itself out.
Got the Office 2013 key in there, just need to get the 2010 key in the system.
Sounds good :)
Thanks for the update.