Revelation 22:18-19 King James Version (KJV)
18 For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book:
19 And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.
Yep, and although they call every thing a translation many are just a paraphase or just words changed
to fit their belief, that is why I like the kj, it appears that he did not care what it said just as
long as we know what it says.
Which means that particular proscription was against adding/altering words to the book of the Revelation only.
Your point has nothing to do with the Gospel of Mark.