I'm not here to tell you that you're making a grave mistake... but I would like to know WHY you want to update from NC2 to NC4.
My understanding is that NC2 was Verizon's development version, which has some pretty nice features that they do not want to general public to have, such as the ability to downgrade to MJE, and the software stubs (or whatever jargon you'd prefer) necessary to allow for kernel modules to be installed. This means the potential for a more open (less locked) bootloader. not necessarily fully unlocked, but at least allowing more wiggle room with kernel mods, but possibly fully AOSP-compatible.
That said... I think NC2 passed all the tests, and NC4 is the one that they released with all the locks in place, for public consumption.
So, I query you once again... why would you want to update to NC4? (A root-enabled release from Beans notwithstanding)