In "All Good Things…", the series finale of Star Trek: The Next Generation, Picard time travels to a number of eras, including his relative future. When the crisis is resolved, he chooses to share what he's learned about the future with the crew.
CRUSHER: You know, I was thinking about what the Captain told us about the future. About how we all changed and drifted apart. Why would he want to tell us what's to come?
LAFORGE: Sure goes against everything we've heard about not polluting the time line, doesn't it.
DATA: I believe, however, this situation is unique. Since the anomaly did not occur, there have already been changes in the way this time line is unfolding. The future we experience will undoubtedly be different from the one the Captain encountered.
RIKER: Maybe that's why he told us. Knowing what happens in that future allows us to change things now, so that some things never happen.
So I see two points here:
- As Data noted, the timeline has already been modified (by the anti-time anomaly not happening)
- As Riker notes, Picard appears to want to further change the timeline by altering the individual futures of the crew (I assume that the falling out between Riker and Worf over Troi was one of them)
With respect to point #2, did Picard violate the Temporal Prime Directive, which likely was codified around this time, by intentionally telling his crew about the future? Wouldn't the proper behavior of the Temporal Prime Directive have been to keep his mouth shut to minimize the number of changes to the timeline?