Focus : The Changing Season

Erase your memory.

On prime time this fall, your favorite character could have a new job. Mom may look a lot different. Or that bouncing baby will have bloomed into a 5-year-old sassy kid.

Over the summer, producers of returning shows have added new characters, gotten rid of old ones or recast leads that just didn’t work out (or left in a contract dispute). It’s all in the name of keeping their series fresh.

Programmers were still juggling their lineups late last month. ABC moved “Home Improvement” to Tuesdays at 9 p.m. after NBC moved “Frasier” to that time slot. ABC’s “Roseanne” will move to “Home Improvement’s” old slot, Wednesdays at 9 p.m. And more time changes could be on the way as the season prepares to launch.

A peek at this fall’s newly changed--and possibly improved--returning shows:

ABC

Boy Meets World: Cory (Ben Savage) starts high school, where he will have a young and worldly homeroom and English teacher (Anthony Tyler Quinn). Fridays at 8:30 p.m. Premieres Sept. 23.

The Commish: Tony Scali (Michael Chiklis), wounded at the end of last season, faces spending the rest of his life in a wheelchair. Saturdays at 10 p.m. Premieres Sept. 24 .

Ellen: The show gets a new day, new title and new comic foil. Joely Fisher plays Paige Clark, Ellen’s best friend. “I’m a planner and a schemer,” Fisher says. Why add to an already large cast? “We needed another strong comic presence,” says executive producer David Rosenthal. Fisher’s take on how she will play off star Ellen DeGeneres: “One of my friends has already called me Rhoda.” Wednesdays at 9:30 p.m. Premieres Sept. 21.

Lois & Clark: The New Adventures of Superman: Expect more suspense and an emphasis on guest villains, a la TV’s “Batman.” Justin Whalin replaces Michael Landes as Jimmy Olsen, and society columnist “Cat” Grant (Tracy Scoggins) is gone. John Shea will appear as Lex Luthor in guest shots only. Sundays at 8 p.m. Premieres Sept. 18.

NYPD Blue: Last year’s breakout star, David Caruso, will leave the series after the first four episodes to pursue a film career. Jimmy Smits (“L.A. Law”) fills the void. Tuesdays at 10 p.m. Premieres Oct. 11 .

Thunder Alley: She’ll still raise the three little tykes and spar with her dad (Ed Asner), but Mom’s taken on a whole new look: Robin Riker (“Shaky Ground”) replaces Diane Venora as opinionated Bobbi Turner. Producers wanted a “strong comedic actress” who’s done a sitcom before. “I never saw Diane’s performance, but chose to keep it that way,” Riker says. Watching a predecessor “can be a help and can be curse.” Also new: a teen-ager who hangs around Gil Jones’ auto garage. Wednesdays at 8 p.m. (New time). Premieres Sept. 14 at 8:30 p.m., moves to regular slot a week later.

CBS

Dave’s World: Dave (Harry Anderson) now works out of a home office, with Mia (J.C. Wendel) as his assistant. Mondays at 8:30 p.m. Premieres Sept. 12.

Hearts Afire: Yes, this show was once a comedy about Washington politics. Now a bundle of joy is on the way: Georgie Anne (Markie Post) has her baby, but she’s not your typical mother. Also, Billy Bob Thornton moves out of their house and gets his own place. Saturdays at 9:30 p.m. (New day and time). Premieres Sept. 24.

Northern Exposure: Rob Morrow, who stars as Dr. Joel Fleischman, is signed for the entire year, but there were doubts whether he’d stay for the entire season. Like Caruso, he has his sights on a film career. Mondays at 10 p.m. Premieres Sept. 19.

Rescue 911: The show takes a cue from Irwin Allen and features more adventurous stories, such as a shark bite, a runaway car and a train wreck. Tuesdays at 8 p.m. Premieres Sept. 20.

FOX

Beverly Hills, 90210: With Shannen Doherty gone, they need someone to stir things up: Tiffani-Amber Thiessen, late of “Saved by the Bell: The College Years,” as a “beautiful, smart and complex” Walsh family friend who ends up living with them. (See With an Eye On ... Page 84.) Jamie Walters (“The Heights”) joins as blue-collar worker Ray Pruit, Wednesdays at 8 p.m. Premieres Wednesday .

Martin: Martin (Martin Lawrence) gets a new time--and a new job--as the host of a TV talk show, where he works under a demanding new boss (Angelina Estrada). A sign the characters are getting older: The cast will be hanging out at a yuppie bar, and Martin will tie the knot with Gina by season’s end. Thursdays at 8 p.m. (New day). Already premiered.

Melrose Place: Super-model Kathy Ireland visits in four episodes as a woman Jake (Grant Show) rescues from an abusive husband. “She’s a very troubled woman,” says Ireland. Executive producer Darren Star is not sure if Ireland will become a regular, but thinks audiences will be tantalized by Ireland. “We tend to think of her as the ‘Bond girl’ of Melrose Place,” he says. Jason Beghe comes back as Matt’s romantic interest and Jane will get a new boyfriend (Andrew Williams). Mondays at 8 p.m. (New day and time). Premieres Sept. 12.

NBC

Blossom: Finola Hughes becomes a regular as Nick’s (Ted Wass) new love interest, with Courtney Chase as her daughter Kennedy. Joey (Joey Lawrence) will be off and about playing minor league baseball, but don’t worry. Producers promise he’ll be in every episode. Mondays at 8:30 p.m. Premieres Sept. 26.

The Fresh Prince of Bel-Air: Last year, Philip (James Avery) and Vivian (Daphne Maxwell Reid) had a baby. Now he’s a 5-year-old (Ross Bagley), ready to blurt out wisecracks. Mondays at 8 p.m. Premieres Sept. 19.

The John Larroquette Show: Alison La Placa (“Tom”) joins as nurse Catherine Merrick, who captures John Hemingway’s attention when he moves in across the hall from her apartment. Bill Morey, who plays Oscar the bum, becomes a regular. Tuesdays at 9:30 p.m. (New time). Premieres Sept. 20.

Homicide: Life on the Street: Isabella Hoffman joins as Lt. Megan Russert, the first female appointed as shift commander. Jon Polito has left the show. Fridays at 10 p.m. Premieres Oct. 21.

Law & Order: Michael Moriarty has left, but Sam Waterston (“I’ll Fly Away”) will take his desk at the D.A.’s office. Waterston’s prosecutor will be charming “but unapologetic,” says executive producer Dick Wolf. Wednesdays at 10 p.m. Premieres Sept. 21.

seaQuest DSV: Less science, more sci-fi. Some story lines: ESP, genetic engineering and time travel. “If people want to learn about seaweed--God bless them--let them watch the Discovery Channel,” executive producer Patrick Hasburgh says of last season’s shows. Gone is Stephanie Beacham. New cast members include Peter DeLuise as Dagwood, the ship’s janitor who comes from a genetically engineered race known as “Daggers,” and Rosalind Allen as a biophysicist with ESP. Sundays at 8 p.m. Premieres Sept. 18.

Sisters: Daniel Gerroll gets a recurring role as an unscrupulous psychiatrist who counsels Georgie (his real-life wife, Patricia Kalember) after her son goes through a rebellious phase. Saturdays at 10 p.m. Premieres Sept. 24.

Wings: Alex (Farrah Forke) has been written out. But Amy Yasbeck joins the show as Helen Chappel’s (Crystal Bernard) snobbish older sister, who comes to Nantucket Island when her charmed life comes apart. “Her agenda is, ‘I’m not here yet. Get off the island,’ ” says Mark Reisman, executive producer with Howard Gewirtz. Tuesdays at 8 p.m. (New day and time). Premieres Sept. 20.

Finally, Frasier returns with only a subtle change to the show’s story line: Martin’s pooch Eddie is getting fixed. Premieres Sept. 20.