Paul Petersen (The Donna Reed Show 1958-1966) had a brief singing career that began during the run of the show. He had two hits on the Billboard Top 40 in 1962. Petersen is still among us at age 76.
Johnny Crawford (The Rifleman 1958-1963), from Wikipedia: "Crawford had a brief career as a recording artist in the 1950s and 1960s. He continued to act on television and in film as an adult. Beginning in 1992, Crawford led the California-based Johnny Crawford Orchestra, a vintage dance orchestra that performed at special events." Crawford died just 3 months ago, age 75.
Rick Nelson (The Adventures of Ozzie and Harriet 1952-1966) was a major pop star with 35 hits on the Top 40. He was killed in a plane crash in 1986 while on tour.
If no one comes from the future to stop you from doing it then how bad a decision could it really be?
Danielle Brisebois, who was a regular on All in the Family in its later seasons and on its spinoff, Archie Bunker's Place (playing Edith Bunker's young niece Stephanie, kind of a Shirley Temple-type to Archie's Lionel Barrymore), became a singer snd songwriter, and in 2015 earned an Oscar nomination for Best Original Song on a co-written work.