The way I remember it is this-
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Barnabas does change history in the sense that Quentin's ghost is no longer haunting Collinwood upon his return to the present. In fact, he prevents Quentin's death, and Quentin (who becomes immortal as well as a werewolf during the 1897 storyline) eventually shows up at Collinwood as another "cousin." By this time it is apparent that the Q man is Chris Jennings' great grandfather, this is how Chris received the werewolf curse.
I don't believe we see Ned Stuart again, once Barnabas returns to 1969, but Chris is not cured of being a werewolf. Sabrina regains her reason, and gets a better hairdo. She and Chris aren't back to where they were before she witnessed his transformation, but it seems like they are again a couple. If memory serves, we don't actually see much of Chris in the rest of the series, which is too bad IMHO.
So yeah, Barnabas changes things and saves David, which was his original purpose in going back into the past. But it's unclear whether or not he does anything to alleviate Chris Jennings' difficulties. Does that help?
