All in the Family seems to have the most examples of Actors playing different characters.

The guy who plays Barney Hefner was Sargeant Pulaski when Archie gets locked up. Frank Lorenzo (Vincent Gardenia) was Jim Bowman and The husband in the swingers episode. The guy who plays Mr. Munson played a character named Barney in an early episode. (I think it was the one with Mike and Gloria's friend Roger) Archie's boss, Mr Sanders (Sorrell Booke) first appears as the station manager when Archie gives the editorial about gun control. Mildred "boom boom" turner was original Archie's friend Duke's wife Bobby Jo.

Anyone remember any others?

and Marten stewart who played Georges Brother.actually played George jefferson before original one came abord.shermen hemesley.that all i know

In the episode Mike's Mysterious Son the lady that plays the little boys mother, also played Maude's daughter, Carol in the episode Maude

Before actor Burt Munson played Justin Quigley, he made an appearence in the first season as a nightwatchman where Archie worked.
Actress Jeannie Linero played a nurse in "Archie Gives Blood", then later played a waitress in "Edith's Problem" ("It was hot when I brought it.")

and Marten stewart who played Georges Brother.actually played George jefferson before original one came abord.shermen hemesley.that all i know

There was an episode where Henry (played by Mel Stewart) impersonated George, because George didn't want to have dinner in a white man's house. But Stewart never played George; George was always played by Sherman Hemsley.

yea, that was the first season one where Archie & Edith are supposed to have dinner with the Jeffersons at their house, (I think Edith accepts the invitation) but Archie calls and says that Edith broke her ankle, so the Jeffersons come over to the Bunkers instead.

Before actor Burt Munson played Justin Quigley, he made an appearence in the first season as a nightwatchman where Archie worked.
Actress Jeannie Linero played a nurse in "Archie Gives Blood", then later played a waitress in "Edith's Problem" ("It was hot when I brought it.")
it's Burt MUSTON not Munson

Got the names from a website. Confusion because Munson, the character on All in the Family, had the first name Bert. Going through the list of characters and the cast names alongside them and it becomes confusing when the names are similar (Bert Munson character and Burt Mustin actor).

and Marten stewart who played Georges Brother.actually played George jefferson before original one came abord.shermen hemesley.that all i know
Actually, he never played George, the character was Henry all along, but he pretended to be George until Louise finally "fessed up" that her real husband refused to walk into a "white" house and that "George " was really her brother Henry