This is an example of NWT translating Jehovah when the Origional word was not Jehovah. 

Am I saying that David couldn’t have written Jehovah instead of Elohim? No. Am I saying that we couldn’t conclude that Elohim is Jehovah? No. 

So what’s my point?  Well the point is, we have an English translation and we do not know Hebrew and Greek. We are trusting that we are reading an honest translation when we read the Bible in our own language. The words should be actually translated the way God inspired them. I’m sure you agree!

What effect can these changes make in this case?

When NWT uses Jehovah in places that should read “God” or “Lord” (Elohim or Adonai) they are sending the message to their JWs that Jehovah is the only way to refer to God. They also hide the reality of the underlying words.  They don’t want the JW to discover that Elohim is a plural word for a single God. They don’t want the JW to think that other Christians are acceptable when they refer to God as anything but Jehovah. 

They also add Jehovah to the New Testament when it is not present at all in the Greek. It’s just the truth. If it was there, we would have it in our Bible at least in the form “LORD” like the OT. But it’s not there. And it shouldn’t be added. Nothing against the name of Jehovah. It’s about being true to his inspired word as it was originally written.