Pilots (https://tvtropes.org/pmwiki/pmwiki.php/Main/Pilot) are often shot long before a show is picked up. What are some examples of big changes (https://tvtropes.org/pmwiki/pmwiki.php/Main/DroppedAfterThePilot) - changes in cast members’ appearance or to the set or what have you - between the pilot and the next episode?

Selfie - For the subsequent episodes, Karen Gillan used a more natural wig, made out of the hair she shaved off for the first Guardians of the Galaxy movie, instead of the ugly wig she wore as Eliza Dooley in the pilot. Also, Henry Higgs's peer Ethan was removed from the cast, and his personal assistant Charlie was added to the series.

The Brady Bunch pilot was filmed in the fall of 1968, a full year before the show premiered. The kids are noticeably younger than they were in the second episode, which filmed in the summer of 1969. And of course, they hadn’t built a set yet so they had a different house.

Eight is Enough filmed its pilot in the spring of 1976 and didn’t start filming regular episodes until January, 1977. Adam Rich looked particularly young in the pilot, and three of the actors playing the children were replaced prior to filming the second episode.

A lot of people are aware of the two Becky's on Roseanne. But in the Roseanne pilot, there was a different DJ, so the series had two DJ's too, albeit one for only episode.

https://www.imdb.com/title/tt0688832/?ref_=nm_flmg_act_1

The Who’s the Boss pilot was done in November 1983 almost a year before it actually debuted.

The Friends pilot must have been filmed quite some time before the 2nd episode. They all look different (hair styles) in the 2nd episode.

The Brady Bunch for sure
Lost in Space
Gilligan's Island
The Flintstones
The New, Original Wonder Woman
Family Affair