Stephen King’s The Gunslinger was revised and expanded.
Patricia C. Wrede’s Talking to Dragons from her Enchanted Forest Chronicles series was the first written as a standalone, but is chronologically the last. Wrede published a re-written edition with alterations to made it fit in properly with the lore, style and characterizations of the other books.
Nitpick: Gilliam forced Universal to release his version by screening his cut for critics prior to the release. After the Los Angeles Film Critics Association awarded his version Best Picture of 1985, Universal caved and released Gilliam’s approved 132 minute version (although not the original 142 minute cut that was released in Europe). But when Universal sold the film to television, it was the “happy ending” version. I believe the Criterion Collection editions contain both cuts (Original 142 minute international version and 94 minute TV version)
What reasons? (I never read her stuff.)
I suppose it’s actually the same reasons - to make them more relevant to modern readers. There’s none of Judy Blume’s education-through-story in Blyton though.
This suggests that the rewrites were a failure, and they went back to publishing the originals again!
So you might say you had some great expectations it would be mentioned in this thread? 
I’ll show myself out.
There was a Star Trek novel called Probe (about the Whale probe from Star Trek IV) that had been substantially rewritten by someone else prior to publishing to the point where the author on the cover disavowed the book. I am 90% sure they eventually did publish the original version (possibly as an online extra, I don’t remember).
The complete 650+ page Adventures of Huckleberry Finn has been printed. I bought a copy at the Mark Twain museum.
He’s also annoyingly done this to The Man Who Folded Himself multiple times. The original is one of my favorite time travel stories. The revisions not so much.
I believe in the first edition of the Goblet of Fire by JK Rowling, she messed up the climactic moment where ghosts came shooting out of the wands of Voldemort and Harry when they fight.
It was supposed to have people most recently killed by Voldemort come flying out in reverse order of their deaths, but the ghosts/spirits came out in the wrong order. James came out before Lilly, which is actually not quite right.
It was noticed by readers and she corrected the error. In the fixed version, Lilly comes out first and tells Harry that James is coming. (I think that is right, anyway).
Rowling credited the error to writer’s fatigue.
See post 3.
See post 26.
He also put out a revised and expanded edition of 'Salem’s Lot that was illustrated (lots of dark B&W photographs) and had a bit more on the townsfolk, Hubie Marsten and Fr. Callahan, IIRC.
I wish I still had my first edition of Roald Dahl’s Charlie and the Chocolate Factory, before the Oompa Loompas were changed in the name of “political correctness.”
Joe Haldeman put out a revised edition of The Forever War, with some stuff cut for the initial release, especially about social breakdown on Earth. He also revised the dates to put it further in the future.
Conan Doyle did something similar. The climax of the first Holmes novel, A Study in Scarlet, has a (to my mind) minor plot hole. It was fixed in the second novel, The Sign of the Four, which opens with Holmes and Watson discussing the recently published A Study in Scarlet. Holmes complains that Watson didn’t just transcribe the events exactly as they happened. Watson argues he used artistic license to make for a better read. To which Holmes replies, basically, “But because you changed the location where we arrested the bad guy, then [description of plot hole]'”
James Branch Cabell republished his books in a uniform edition of 18 volumes, the Storisende Edition. Used to be nearly impossible to find, I’ve only found it in one library.
How about Lawrence Block’s stories about the young woman who murders everybody with whom she has sex? When he collected/expanded them into a novel, he changed around several details of her background, like whether she murdered her parents.
I read a copy of Agatha Christie’s “A Mysterious Affair ar Styles” - the very first Hercule Poirot book. There were two versions of the ending. One which followed from the penultimate chapter. That was the published version from 1921. The other was an unpublished version that was scrapped but the publisher included it at the end.
JK Rowling saying that Hermione might have been black probably counts.
In the original London theatrical version of The Cursed Child, Hermione was played by a black woman. It is not at all uncommon in theatre for white characters to be played by black actors - it’s just a thing. Hamlet has been played by black men, and by women, too, with no changes made it the character, and nobody’s saying that Hamlet, Prince of Denmark, was black or male.
Sometimes it’s a plot point - Hamlet’s an outsider, after all - but sometimes it’s genuinely colour-blind: secondary characters are also often played by non-white people despite it being highly unlikely they were written as non-white, and nobody cares. It’s a theatre thing. (In the UK - can’t guarantee the case for the US or elsewhere).
Hermione in the books was white, and there are a dozen in-text instances where that’s obvious, plus Rowling’s own drawings of Hermione. There was no need for Rowling to try to claim that Hermione had been black all along just because a black actress had been cast to play her in a play adaptation.
I suppose that sort of counts with the OP asking about a publisher making changes, but the author never did.
Don’t blame him. The original is in some anthology I have and it’s not very good.
They changed the names of some of the Faraway Tree characters because they two of them were called Fanny and Dick, but I could cope with that in the 80s when they were already funny, and so could my daughter. You giggle, and carry on reading.
They also got rid of some of the mild racism, which I would prefer to keep in so that kids know that stories were like that then. It wasn’t traumatic racism that would hurt kids as they read it, and it’s not good to pretend that the characters, even the good guys, in 1930s-50s stories were completely non-racist.