An interesting take on what seems will always be an everlasting point of contention!
Certainly, almost all scholars are in agreement that the NWT's rendering of the second part of the statement as "and the Word was a god" is taking excessive liberties.
However, determining what the Bible writer actually meant in John 1:1 does require more than a superficial understanding of the grammatical structure and nuances of the Koine Greek language - particularly as to how this relates to the use (or not) of the definite article.
For example, Daniel Wallace, in his Greek Grammar Beyond the Basics, includes an complete 50 pages dealing entirely with just with the use of the definite article. (This section is entitled "The Article - Part 1"). Furthermore, he then goes on with a further 15 pages that apply directly just to John 1:1. The outcome of this dissection of that verse is very much one of "nature and essence" rather than identity:
- i.e. The Bible writer is here saying that "The Word" is of the same nature and essence as God, but he is not saying that "The Word" and God are one and the same being (not in this verse, anyway!).
Given this, it would seem very few translations of The Bible render John 1:1 correctly. Most render the second part as ".... and The Word was God." According to most informed commentators of the Bibilcal Languages, that is no more correct than the New World Translation's "and the Word was a god".
Just saying, anyway! (Certainly don't intend to re-open the 2000 year old dispute over whether or not God is a Trinity)