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:
 And if any man shall take away from the words of the book of this prophecy, God shall take away part out of the book of life, and out of the holy city, and from the things which are written in this book.
As these two scriptures relate to 'prophecy' some ministers
advise adding or taking away would be acceptable.
Our question? Why would they want to change anything?