And as a result of watching so many shows in their entirety, I've come to realize quite a few of my favorites were actually midseason replacements, which typically meant they were something the network ended up giving a shot because what they had banked on tanked.
Usually this isn't noticeable beyond a shortened first season. But occasionally it's resulted in early episodes that don't entirely match the show I came to know and love.
Here are a few that surprised me, including one classic that replaced another classic on its way out:

"These Friends of Mine" (replaced "Grace Under Fire"): First off, I would have bet money this and "Friends" both premiered in the fall of 1994, and I would have lost. I'm reading now that they switched its title to "Ellen" to avoid confusion when the NBC show debuted, but my memory is that it was changed because all three of THESE FRIENDS of hers were fired from the show -- two immediately (Holly and Anita), one later (poor Adam, who wound up being the Cindy Snow of the series) -- hence making it all "Ellen." (How prophetic!) The addition of Paige and Spence largely worked, although they went overboard with Joe and Audrey, who were best in small doses.
Note: It's worth checking out "The Ellen Show," her short-lived follow-up she created with Carol Leifer (of "Seinfeld" fame) and Mitchell Hurwitz, where you also get to see the late/great Cloris Leachman and Martin Mull -- even if the person who plays Ellen's sister is inexplicably 16 years her junior!
Claim to shame: I vividly remember reading the description of "Friends" (in probably Entertainment Weekly) and cracking up that anyone would think a show starring Alex P. Keaton's girlfriend would be successful.
"Twin Peaks" (replaced "The Young Riders"): When David Lynch died I decided to give this one another try -- and a "try" I did. My friend Lynn actually warned me as I (re)started watching that this had been a midseason replacement and the infamous dive in quality paralleled the end of its initial eight-episode run. Note: Even though Damian considers himself a fan, he put the brakes on the rewatch about halfway into the second season. (Yikes.)
"Parks and Recreation" (replaced the American "
Kath & Kim." which I think I'm the only one who liked): I previously mentioned that I quickly dropped "Parks and Rec" when it first came out; but the bottom line is the show started out horribly and then got delightfully retooled when Amy Poehler's Leslie Knope went from cringeworthy Michael Scott impersonation to grownup Tracy Flick homage. (Can't say I wasn't bummed to not get a little more Mark Brendanawicz, though!)
Wikipedia notes that "Parks and Recreation" was in fact a midseason replacement in its first, third and seventh seasons. It was brought back as a midseason replacement in the third season (to accommodate Amy Poehler's pregnancy) and in its season finale to meet contractual obligations.
"Kate and Allie" (replaced "AfterMASH"): Other than the recasting of Kate's ex-husband, Max -- from John Heard to Harley Venton -- things didn't change too much. What surprised me was learning that the show -- originally called "The Mommies" that Susan Saint James "seized up" as a way to stay on the East Coast -- was so popular after just six episodes that it was picked up for a full second season. And that the show itself became a midseason replacement at the start of its sixth reason when unsupportive network bosses took over and removed it from the fall schedule. (Saint James
was duly bitter while discussing it at the time on a episode of David Letterman!)
"Three's Company" (replaced "The Tony Randall Show"): I was reminded that this also got picked up after just six popular episodes by watching "Behind the Camera: The Unauthorized Story of ..." the other week. I'm sure I'm not the only one who's noticed that Suzanne Somers's Chrissy Snow changed almost completely once the show returned and got into a groove -- from the platinum hair and snorting laugh to her plunging necklines and equally plunging IQ!
"Don’t Trust the B—— in Apt. 23" (replaced "Happy Endings," which itself had replaced "Mr. Sunshine"): That there were only seven episodes in its midseason run makes it an even bigger travesty that the show got canceled the following year.

"Watching Ellie" (replaced "Three Sisters"): Not even a revamp could save this little-seen but quite good Julia Louis-Dreyfus vehicle where she plays a struggling lounge singer in L.A. (This pre-dates “The New Adventures of Old Christine.”) In fact, changing it from a quirky one-camera show to a more traditional sitcom (with multiple cameras, a live studio audience and an added laugh track) brought the ratings down even more.
They also cut back the role of the creepy super (Peter Stormare as Ingvar) in the second season. and upped Steve Carrell's character, who was the prototype for Michael Scott. (Note: I found this on YouTube.)
"Barney Miller" (replaced "The Odd Couple" -- can you imagine?!): I remember disliking this series as kid because it all took place in one room, so the irony isn't lost on me that the original 13 episodes were markedly different from the rest of its run, featuring life with Barney's wife who also used to stop by the 12th Precinct. (Liz was played by the venerable Barbara Barrie, who later popped up on Season 2 of my youthful fave "Double Trouble," which was also a midseason replacement, twice!)
In addition to axing the domestic angle, Det. Janice Wentworth was also disappeared a while later., which of course was done so Linda Lavin could star in "Alice."
"Eight Is Enough" (replaced "Rich Man, Poor Man: Book II"): This was perhaps the saddest reason a show had to be revamped, as Diana Hyland, who played the mom on the first abbreviated season, died of cancer at age 41 on March 27, 1977, two days before the third episode even aired. (Also of note: In the pilot, David was played by Mark Hamill, Nancy was played by Kimberly Beck, and Tommy played by Chris English. When ABC picked up the show, Grant Goodeve, Dianne Kay and Willie Aames were recast.)
Footnote: Betty Buckley, of course, came on in Season 2 as stepmom Abby. But what was never addressed was the fact that she was actually slightly younger than Laurie Walters -- who played daughter Joanie, who wasn't even the eldest kid or even the eldest daughter! -- and not much older than most of the other children.
"The Office" (replaced "Committed"): Pretty sure the original season was all but line-for-line adaptations of the British original, which of course only ran for 12 episodes and two specials, compared with 201 episodes over nine seasons in the U.S.
"Happy Days" (replaced "Temperatures Rising"): The early episodes are noticeably different because of the single-camera setup and focus on “innocent teenager” Richie, which is to say nothing of brother Chuck. Funny to recall how popular 1950s nostalgia became in the 1970s considering the fact that its silver screen fraternal twin,“American Graffiti,” was actually set in 1962.
“Angie” (replaced “What’s Happening!!”): This started out strong but quickly seemed to suffer from what has been described as the “Rhoda” problem: The single-gal protagonist lands her dream man in the first episode and then they don’t know what to do with her. After having Angie working in a coffee shop at the beginning of the series, the producers decided now as a doctor’s wife it would be more plausible for her to become the owner of the joint. (They also had the couple suddenly move to a new home.) And when that didn’t work, they had Angie sell the coffee shop and buy a beauty salon so her mom (aka the Italian Ida Morgenstern, played by non-Italian Doris Roberts) and sister could get more screen time. The only good thing to come out of this was the addition of cocky stylist Gianni (Tim Thomerson), who wore the tightest pants to ever appear on network television.
Others:
"All in the Family" (replaced "To Rome With Love")
"Laverne & Shirley" (replaced “Welcome Back, Kotter")
"Moonlighting" (usually an ABC Sunday Night Movie)
"Dawson’s Creek" (syndicated programming)
"Happy Endings" (replaced "Mr. Sunshine")
"A.P. Bio" (replaced "The Good Place")
P.S. It turns out there was a podcast called "
The Mid-Season Replacements Podcast" -- I stole its logo -- hosted by Randy Dankievitch and Sean Colletti, although it seems to just be about television in general.