Right now, I want to allow my customers to transfer the key from an old computer to a new one. I want to give them the ability to deactivate and then activate it again. All of this should be done from a new computer.
No, you'll have to manually deactivate their key for them. In the near future LicenseChest will be out (giving you control over whether customers can “remotely deactivate” keys, and how many times they can do it.).