AI believe that this is referring to one who is selective about which parts of the Bible are the Word of God because he or she doesn’t want to accept all of it. Could it be as literal as someone “printing a bible with missing verses, etc.?” Yes, it could include that. But I think it there are more subtle ways of subtracting from the Word of God. Here is the text:
“And if any one take from the words of the book of this prophecy, God shall take away his part from the tree of life, and out of the holy city, which are written in this book.” (Rev. 22:18-19)
Note that the term “book of life” should really be translated “tree of life”. The tree of life is a picture of Christ Himself (raised from the dead as the head of the New Creation) and the holy city is a picture of the Church. The one who discounts portions of God’s Word will not have a part in Christ or His Church.
Also, where is says “and from the things that are written in this book” the words “and from” have been added (not to pun) by the translators. So if you read it without them you get more clearly the meaning: if any man takes away… etc., then God will take away his part in Christ and the Church, which are written in this book. So, the “things written in this book” ARE Christ and His Church.
The question then is, if the penalty is eternal separation from Christ and the Church, can this happen to a real believer? I would call on the many other scriptures which say we can never lose our salvation, e.g. John 10:28: “I give them life eternal; and they shall never perish, and no one shall seize them out of my hand.” Therefore, Rev. 22:19 must refer to a person who was never a real believer, but one who only had had a part in Christ and His Church by profession, not in reality.
One more thing… what are “the words of the book of this prophecy”? Is it just Revelation, or the whole Bible? I’m not sure. Me feeling is that “this book” is specifically Revelation, but that in principle it includes the whole Bible. One thing that I believe supports this possible meaning is that the Book of Revelation is written to the Church, to address the ruin of the Church, and to have a moral effect upon her conscience. If someone tampers with any book of the Bible it will likely be with the one that hurts their conscience the most! A good reason why the principle of Rev. 22:19 might encompass the whole Word of God is that Revelation ties together many other books of the Bible, including Old and New Testaments. If you tamper with this book, you tamper with them all.
I think that there are those like Joseph Smith the founder of the Mormon System who had made a so called translation of the Bible. ( I saw one years ago in a public library in Lebanon, MO) This Bible is so full of error relating to their system and probably was partly from the KJ as this man had no ability to translate from original languages. He intentionally both added to the Word of God and took away from the Word of God doing the work of the enemy Satan. We know Joseph Smith both as and Apostate and of course a unbeliever.
In order to justify “new revelations”, the Mormons must first discredit the authenticity of the Christian canon. By arguing that the Bible became corrupted down through the centuries, they attempt to justify “another testament of Jesus Christ”. Like you say, they not only take away from the Word of God, but also add to it. Sad that nearly 15 million people today are being led astray by Mormonism.