I warn everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues described in this book, and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book. (Revelation 22:18-19)
These words are certainly a very serious warning indeed against tampering with the Book of Revelation — either deleting any of it or adding to it. There is a similar warning in Deuteronomy 4:2 not to tamper with the books of the Law. As the words of Revelation 22:18-19 occur at the end of the completion of the New Testament, perhaps they apply to the whole Bible. It is difficult to imagine that anyone who believed that the Bible is the inspired word of the Lord God would want to tamper with it anyway.