I don't like the idea that some insignificant event has major repercussions, and therefore that event must be changed / preserved. Even in real history, when you look at minor events that caused major changes, there is a broader context. The momentum of history will push things in a certain direction. You can't point to a pebble in a raging river and say that pebble is altering the flow. If event X hadn't lead to the event, then it would have been something else.

Besides that, if you're going to use time travel to solve a problem, then just tell the people what they need to do. Don't be all vague about it.