How to change the product ID in Office 2007 64 bit

Open registry editor.
Browse to HKEY_LOCAL_MACHINESOFTWAREWow6432NodeMicrosoftOffice12.0Registration
Under this there is a subkey that is a long GUID.  Click on that and find the following keys.
DigitalProductID & ProductID
Delete them both.
Once these are deleted open any Office application and it will prompt you for a new key.