Suck Sessor: A variation, since aside from the whole bit about being a traitor and a murderer she's actually an extremely competent officer.
Suspiciously Similar Substitute: For Lt. Saavik from films II-IV, plus Commander Xon from the unmade Star Trek: Phase II TV series, in that they're both Vulcans who are set up to succeed Spock.
Tempting Fate: She suggests serving Romulan Ale during the meal with the Klingons, which given the underlying tensions between the two peoples and the extreme strength of Romulan Ale, goes over about as well as you'd expect. Of course, this is part of a Xanatos Gambit to make it later look like Kirk attacked Gorkon's ship in a moment of drunken rage.
What Could Have Been: If she had been Saavik as originally planned, rather then being made into the aforementioned Suspiciously Similar Substitute, it would have been a lot less obvious, and indeed rather shocking, who the traitor on the Enterprise was. As it is in the finished film, with her being the only new major character on the Enterprise... Well, it isn't like they would have made Spock, Scotty, Uhura, or Chekov the traitor! Process of elimination really only left Valeris as the audience's only suspect.
Spanner in the Works: He persuades the judge at Kirk and McCoy's trial to sentence them to exile on Rura Penthe rather than giving them the death penalty. It's subtle, but you can see that Chang is not pleased by this development, and it allows Kirk to escape and foil the conspiracy.