James Cameron has been asked this a few times in the past weeks to the release of the movie, and he has said he did not want to change anything about the movie past adding 3D. However, it seems he admits to making a change while interviewing with a British magazine Culture. James Cameron resisted temptation to cut scenes he was no longer happy with when preparing to re-release his blockbuster film Titanic in 3D, [however...]
Neil deGrasse Tyson, who is one of the U.S.' leading astronomers, sent me quite a snarky email saying that, at that time of year, in that position in the Atlantic in 1912, when Rose is lying on the piece of driftwood and staring up at the stars, that is not the star field she would have seen, and with my reputation as a perfectionist, I should have known that and I should have put the right star field in.
So I said, "All right, you son of a bitch, send me the right stars for the exact time, 4:20 a.m. on April 15, 1912, and I'll put it in the movie," Cameron said. "So that's the one shot that has been changed."