Tracy Shaffer, a managing director at PMK/HBH, has left the public relations firm to become entertainment director of Cosmopolitan magazine.Shaffer’s exit is unrelated to last week’s firing of praisery prexy Leslee Dart. Shaffer had actually given notice prior to the Dart move, but the agency will have to shore up her client list as well. Shaffer repped Kevin Bacon, Billy Crystal, Johnny Depp, Paris Hilton, LL Cool J, Charlie Sheen and Aaron Sorkin, among others. Shaffer, who’d been at PMK since 1994, said she wanted a change of venue. Working under editor-in-chief Kate White, Shaffer will use her connections to land big stars for cover stories for the Hearst Corp.-published monthly. She begins at the mag on Nov. 29.