If being a TV programmer is like being a gambler, the trick is knowing when to hold ’em, when to fold ’em and, apparently, when to just shuffle the cards.

With millions invested in a new series, studios seem more intent on fixing or revising existing shows than on canceling them and cutting their losses – particularly if they have faith in the talent involved.

Several recent examples can be found, including three ABC series: “Ellen,” which has undergone a series of changes in its short life; “Blue Skies,” which eliminated most elements of the show, kept three supporting players and, with the same producers, introduced a new series, appropriately titled “A Whole New Ballgame,” starring Corbin Bernsen; and, most recently, “All-American Girl,” where the studio will use a regular-season episode to create a pilot for a possible new series featuring the star, stand-up comic Margaret Cho, and Amy Hill, who plays her grandmother.

Similarly, NBC pulled the plug on “The Martin Short Show” but turned that deal into a sketch comedy starring Short, which should get a tryout this spring; Warner Bros, and Miller-Boyett Prods, asked to shelve “On Our Own,” and will bring the ABC comedy back with a new character, and Spelling TV turned over the cast in Fox’s “Models Inc.” trying to get that serial speeding down the runway.

Even the critically acclaimed “Homicide: Life on the Street” underwent a makeover this season, adding and deleting various characters in an effort to boost the gritty cop drama’s appeal to women. ABC’s “Thunder Alley” also changed female leads after its first season.

Disney, the studio behind “Ellen” and “All-American Girl,” has been one of the most aggressive in trying to fix perceived problems through producer and/or cast changes.

In the case of both series, part of that resolve stems from a belief that the leads – Ellen De-Generes and Cho, respectively are genuine TV stars who weren’t being fully served or exploited by their shows.

“We believe in Margaret,” says Disney TV & Telecommunications network prexy Dean Valentine, explaining the somewhat novel move of creating the alternate series concept. He acknowledged that “Girl” has done reasonably well in the ratings but hasn’t proven a spectacular vehicle for Cho.

Shooting the pilot “seems to give me a two-for-one shot” at making ABC’s schedule next season, which is a real challenge given the general strength of the net’s primetime roster.

There are risks associated, as well, in cutting stars loose, since there’s no guarantee they’ll be available for your next project. Take the case of Bruce Campbell, who starred in “The Adventures of Brisco County Jr.” Fox was more enthusiastic about the actor than the show itself, which was canceled after one season. Unfortunately, so was NBC, which signed Campbell to a holding deal.

Efforts to “fix” a show don’t always work, since viewers often feel they’ve seen a series and can’t be lured back to sample it again. “Most of the time, the ship has sailed,” admits Warner Bros. TV prexy Leslie Moonves, one of the most skilled advocates when it comes to saving existing series. “Once you’ve lost (the audience), it’s hard to get them back.”

Still, there are examples of longrunning shows that caught fire or extended their lifespan by making such changes.

Spelling kept tinkering with “Melrose Place,” for example, till Heather Locklear’s character arrived and pushed the show to a new level of success. On the flip side, “Models” – despite several alterations – still gets poor scores from the Nielsen judges.

Warner Bros, has also been extremely able when it comes to making such revisions – some as specific as altering a show to make it more compatible with a new time period. ABC’s “Hangin’ With Mr. Cooper” added moppet Raven-Symone to the cast in its second season, coinciding with its shift from Tuesday to the network’s youth oriented “TGIF” Friday lineup. The series was recently renewed through its 100th episode, considered the magic number for syndication.

Experienced producers like Miller-Boyett, Moonves says, invariably learn how to improve series as the year goes on. “Family Matters,” for example, was a marginal show until Jaleel White turned up in a guest shot – in the midst of its first season – as Urkel, eventually becoming the show’s breakout star. “Their pilots are never as good as the 22nd episode of their shows,” Moonves notes.

One of the studio’s most celebrated changes, in terms of sheer creativity, involved “Gabriel’s Fire.” In the 11th hour, the ABC show metamorphosed from a gritty 9 p.m. drama starring James Earl Jones in its first season into a light-hearted 8 o’clock buddy detective hour entitled “Pros & Cons.”

“That was a great save,” Moonves recalls of the show. “Unfortunately, the save only lasted one year.”