Most of the time, installing a new NK.bin file also includes wiping out the existing one and overwriting it. So unless your new NK.bin file contains everything already on there, then all you would be doing is adding the new stuff and deleting all your important system files....not a good idea.
Sometimes it is just safer to manually copy over whatever it is you want and then when you are done, make a complete system backup of everything in case you have to hard reset.
Unless you have a MP900
where we can actually create a complete custom NK.bin with exactly what ever we want on it.
Another option would be in Viewsonic had an already created NK.bin with everything on it...then you might could just add the drivers/files you want to that and reflash you unit. Seems to me that I used a Viewsonic flash once on my Neta 980 to go from CE3 to 4.2. But I've never seen a CE5 image for the V212.