Seems to me that if they change events by going back in time and DOing something, then that is how the event transpired. In such a case, you would note the history leading up to the "added factor" and might note that all the trends were pointing in one direction and then, suddenly, everything shifted in a negative way. That would be a clue that "meddling" had taken place. A recent example might be the assassination of JFK. You can see where HE was taking the US, and then you can see where the US went AFTER his death and you can think that his death was just such a "meddle." The history is what it is, but you have to look at things on both sides of a node event.
Then there is the factor of "changing history" by obscuring it. This also can be exampled with the death of JFK. We have the Warren report as "official documentation," and then there is the Truth - some of which can be inferred from the many researches done on the matter. Which will survive in "history?" You could say that the Warren report is "planted" to obscure history. That doesn't even have to be done by "time travel," though it is certainly possible that the assassination was achieved by forces moving back in time to make sure that Kennedy was assassinated.
If 4 D forces can't come in and do stuff directly (which I suspect is the case) they CAN "abduct themselves in the past" and program themselves to do certain things. That is a direct manipulation.
STO forces, on the other hand, seem to be limited to giving information to themselves in the past...
An interesting movie to watch to get a handle on some of the ideas is "Frequency." It's slow getting started, but once it gets moving, I think you will be amazed at how deftly it presents the idea of "communication into the past" being able to "change the future."
