I work in support for NX and deal with CIDs all the time. In most cases the CID will not change if updating the OS.
Having said that I have seen a customer system, that switching from the original Windows 7 to XP the CID changes. They then decided to go back to Windows 7 and the CID changes to the first one they had with preinstalled Windows 7.
I also had a laptop, that was upgraded from Win XP 32 bit to Win XP 64 bit, then to Vista 64 bit, then to Windows 7 64 bit over a couple of years. The CID never changed. I then reformatted with Windows 7 64 bit and the CID changed.
I always warn customers, if they ask, to be prepared for it to change. It may not, but it can.
Anthony Galante
Technical Resource Coordinator

NX4.0.4MP10, NX5.0.6, NX6.0.5, NX7.0.1, NX7.5.0-> NX7.5.5 & NX8.0.0 -> NX8.0.1