As mentioned in "Intention vs. Literal Speech", I do not want to get too deeply into the issues of determining whether the "sense" of a message is changed by some action, because therein lies an infinite quagmire of "mere philosophy". Fortunately in the case of concrete communication, especially when using computers, it's quite easy to determine if the concrete message has been changed between the sender and receiver. Simply answer the question "Did the bits change en route?" If yes, the message integrity has been violated. If no, it has not been. In the case of non-computer communication, you can still ask largely the same question by "virtually" digitizing the message and comparing what was sent to what was received, within reason. If the concrete parts are adequately contained in the final message, then everything is fine.
Example of "within reason": A person making a speech in an auditorium won't sound precisely the same to any two people, in the sense that a microphone would pick up a slightly different version of the speech. In this case, we do have to make the reasonable determination that the differences are irrelevant to the contents of the speech, or unavoidable due to the nature of the auditorium. It should not strain anyone's mental faculties to say that everyone is hearing the same speech, unless someone quite deliberately censors it somehow.
Hopefully you can see this is exactly what I defined as censorship, because changes in the concrete parts are the same as changing the message, so this topic is previously covered.