Ask Dr. Waite, the author on the difference between the KJV and the NKJV. I saw his book at the annual conference some long years ago. He provided the informastion concerning this difference between them -- Add various things, Change various things, Non-masoretic text, Non-TR, and Omit various things.
Waite has been shown to be inaccurate, and to the extent that he repeats these things after he has been shown to be inaccurate he is guilty of being dishonest by saying something he knows to be false.
Furthermore you say that it is a good question to ask if text critical methods are biblical. That is a nonsensical question. Scripture never addresses that issue.
Someone on the board mentioned there are about 2,000 differences between the KJV and the NKJV. That sounds about right to me. First there are about 800 words that need updating plus or minus a few, then all of the side-notes were removed in the 1786 revision which were more than a thousand. That is a lot of traps we could fall into.
The NKJV is revised and translated by mostly baptists .All of the translators are well trained in biblical languages. Even the textus receptus is more complete today then it was in 1611 or 1786. Through archaeological finds and research we know more about all of the biblical languages
today then the re visors and translators of 1611 and 1786 did. The English language has changed in 400 years it is far more technical, what are the, over 500,000 English words now, words are far more precise now.