This is to be played like the other “games” of this board where you name just one show per post. You can name the show and mention its cast changes.

I’ll start off…

Cheers
Nicholas Colasanto as Coach in seasons 1-3.
Woody Harrelson as Woody Boyd in seasons 4-11.

Shelley Long as Diane Chambers in seasons 1-5.
Kirstie Alley as Rebecca Howe in seasons 6-11.

Kelsey Grammer as Dr. Frasier Crane in seasons 3-11.
Bebe Neuwirth as Dr. Lilith Sternin-Crane in seasons 7-10. (making appearances in 4-6 & 11)

Everybody Loves Raymond--Only one main addition to the cast (Monica Horan as Amy) midway through the first season.

Doesn't virtually every show have cast changes?

Green Acres

Barbara Pepper as Doris Ziffel; seasons 1-3
Fran Ryan as Doris Ziffel; seasons 5-6

Robert Foulk as Mr. Trendall; seasons 2-4
Robert Foulk as Mr. Wheeler; season 6

Doesn't virtually every show have cast changes?

Then this will be a long thread.

Eight is Enough

Season 1 -
Grant Goodeve replaced Mark Hamill as David
Dianne Kay replaced Kimberly Beck as Nancy
Willie Aames replaced Chris English as Tommy

Season 2 -
Betty Buckley replaced Diana Hyland (who died) as the mother figure of the show.

Mister Ed-Larry Keating as Roger Addison- seasons 1-3 appeared briefly on the first episode of season 4, Edna Skinner as Kay Addison seasons 1-4, left partway through season 4. Jack Albertson as Kay's brother for a few episodes of season 4(made brief appearences in seasons 1-3). Leon Ames and Florence McMichael as Colonel Gordon and Winnie Kirkwood, seasons 4 and 5. Barry Kelly as Carol's Father, season 6(Made brief apperences in seasons 2-5).