The licence can be deactivated from one device and activated on the other at choice, I had a N800 that had been stolen with a navicore licence from my old n770 and Navicore support transferred the licence from the stolen device to the old one again immediately. Very nice support.
The limit is that you cannot use Navicore on both devices at same time, as perfectly explained by jaros quoting the manual. The verification of the key is made online, and so for transferring the licence from one device to another you have to be connected. There is some sort of DRM that check licence serial and associate it with your device (perhaps with the mac address of the device)