I have a Windows Server 2012 R2 machine which has 2 NICs. I have used its Computer ID to generate activation codes for some NI software and I have successfully activated them.
I noticed, however, that if I disable the first NIC (Control Panel > Network and Internet > Network and Sharing Center > Change Adapter Settings > [Right-Click NIC1] > Disable), strange things happen in the license manager.
All of my activated software now says "Unlicensed"
NI License Manager > Computer Information produces a completely different Computer ID than before.
If I re-enable the NIC and restart NI License Manager, everything goes back to normal.
That is expected behavior. First, the Computer ID is generated from your "primary" NIC. Also, when a product is activated then the license for that product is tied to the Host ID of the NIC, which is also used for generating the Computer ID. So, if you remove or change your "primary" NIC then the Host ID will be different and therefore not match up with the Host ID used when the license of the product was activated, and the Computer ID will be different because it is being generated from a different Host ID. You have a few options. Reinstalling the NIC is definitely one of them, but if you want to remove that particular NIC or make a different NIC the "primary" NIC, then you can deactivate the license in order to reactivate it with a different Host ID, based on the new "primary" NIC, which is also used to generate the Computer ID. To do so, open License Manager, go to the Local Licenses tab, right-click on the license you want to reactivate, first select Deactivate, then right-click again and select Activate. To activate all licenses for every product at once, then you can click "Activate Software". At this time there isn't a button or option to deactivate all licenses for every product at once, so that will need to be done one-by-one.