I've seen first hand how it has been used in the real World to completely change the perception of the reader in very subtle ways. Take, for example, a Manifesto. The government decides that an author is a problem to be dealt with. The Manifesto he has written has limited distribution within a close circle of associates. What is done is to get a copy and rewrite it in very subtle ways, so by the time a reader finishes it, the original intent has been deflected or turned on it's head. The next step is to make thousands or Millions of copies that are indistinguishable from the original, except for the subtle change, right down to the type of paper, ink and binding. Even the author, examining a copy in detail would recognize it as his own. By the time he realizes what has happened, he has been discredited and the movement has lost valuable momentum, if not destroyed.

This has been done many, many times, and will be done many times to come, because the Powers That Be have the resources, experience and talent to do it, and they will most likely do it using your Tax Dollars.