and Why did NJS change to Cobham Aviation Services?
It's a world wide re-branding of the Cobham companies. I can't find the official blurb right now but there are benefits in terms of brand recognition in having the companies using the same name. Previously people may have had little idea that NJS was a Cobham company, now the link is obvious, and in some cases that may be beneficial.
BTW, in long form it's Cobham Aviation Services Australia or CAvSA (too close to CASA for my liking) but they're using just "Cobham" in informal use or when the location of the company is not ambiguous.
I can't answer your other questions as I don't work for them.