He did make some changes between the US and UK Editions when he had the opportunity to change some details in the texts. Unfortunately, the text you find in the newer editions nowadays is the one without the changes he wanted.

It is true that Lewis was looking at doing some revisions, but ill health and early death prevented him.
I would guess that he might have reconciled a few of the quirks of dates etc, and maybe done an official timeline (the one we have is from Mr Hooper who knew him for only a few weeks).
I don't believe that the changes made for the American editions were seen as 'improvements' but alterations for a different audience.

One revision I'd like to see might be (in LWW?), some mention of how Narnia's great "Tree of Protection" came to its end. (Surely Tumnus or the Beavers might recall the sad event in legend or song?) Also ... maybe somewhere, a brief appearance in the Professor's house, by a visiting "Miss Plummer"????

Since LWW was the first book written, and many people support reading it first without reference to MN, it seems unwise for this to be mentioned in LWW. Perhaps there are places in later books for it to be discussed - just as there are references to other stories.

It's funny, because I am someone who loves thinking about how to alter a book or film to make it better, but it's the exception with Narnia! I love speculating about how they might be adapted into films, but I never find myself thinking about how to tweak the books themselves; they're almost perfect in my eyes. It's really interesting to hear that he was considering doing some revisions! I didn't know that.

Although it's one of my favorites now, I do remember not liking Prince Caspian as much as the other books when I first read them... I think that's largely due to the odd structure of the book, so that is something that I might consider changing. Usually stories that have multiple perspectives alternate back and forth more. So for better flow, maybe have the chapters alternate between Caspian's POV and the Pevensies' POV instead of the long, Caspian-centric stretch the middle of the book. Actually, next time I re-read PC, I might try reading the first eight chapters in this order:

Chapter 4: The Dwarf Tells of Prince Caspian
Chapter 1: The Island
Chapter 5: Caspian's Adventure in the Mountains
Chapter 2: The Ancient Treasure House
Chapter 6: The People that Lived in Hiding
Chapter 3: The Dwarf
Chapter 7: Old Narnia in Danger
Chapter 8: How They Left the Island

Maybe it'll be the best idea ever, or maybe it'll make my head spin.

To me, quite a few of the details in LWW jar with the rest of the books. For one thing, the Beavers come across as too human. In the other books the Talking Beasts are more like their dumb counterparts in certain ways, such as how they eat, sleep etc. Bree and Hwin, for instance, don't live in houses, wear clothes or eat their food cooked and off plates. So with the Beavers in LWW, I would lose Mrs. Beaver's sewing machine for starters, and alter the meal that they serve to the Pevensies so that while it was still edible for human children, it was more in keeping with what a couple of intelligent beavers might be able to produce (although I'm not sure how to represent this). It would also get round the problem of how potatoes, tea and the hops for Mr. Beaver's beer could grow in the frozen Narnian soil.

I would also remove the "talking down to children" that is present in LWW and not in any of the other books, such as "if I did [describe the Witch's followers], the grown-ups might not let you read this book". That made me squirm when I first read LWW when I was about 6 or 7.

Experiment House always annoyed me a bit. Lewis seemed to imagine every school as a boarding school, yet Experiment House doesn't sound or feel like a boarding school - it's more like a modern State school (which takes day pupils only). It's as if Lewis tried to imagine a modern day school, then absent-mindedly threw in a line about Eustace and Jill going to their dorms to change out of their Narnian clothes.

And yes, I would sort out the English timeline. LWW took place "long ago during the war years", and going by what the children say about how much time has passed in England between the adventures, less than four years passed between LWW and LB, yet Eustace referred to being "smashed up by Britsh Railways", and British Railways wasn't formed (when the railways were nationalised) until 1948.

When I saw the title of this thread I had to do a double take. Here I am thinking Lewis had some obscure addition to Narnia written in Polish.

One revision I'd like to see might be (in LWW?), some mention of how Narnia's great "Tree of Protection" came to its end.

I like that idea, but only if it was subtle in its mention. Otherwise it would definitely be a spoiler for Magician's Nephew. Of course that's probably your point, making all the books read well chronologically. I wonder if Lewis himself would have preferred the chronological or publication order and changed his work accordingly?

Rose-Tree Dryad, if you ever read PC in that order, let us know how it flows. I'm afraid alternating chapters would be jarring because different Trumpkins would be in both timelines, but maybe it would work.

For one thing, the Beavers come across as too human. In the other books the Talking Beasts are more like their dumb counterparts in certain ways, such as how they eat, sleep etc. Bree and Hwin, for instance, don't live in houses, wear clothes or eat their food cooked and off plates.

I can see how people are going to find different things they want to change from the books. I find that scene charming myself. Beavers are second only to humans for altering their environment by building dams. It makes sense they'd be more industrious and have more tools (and I don't think they're mentioned wearing clothes unless I'm forgetting something.) Also Reepicheep always had a sword and circuit on his head. Meanwhile, Hwin and Bree were raised just like dumb horses, so I'm not sure how good of an example they are.

On the same note, I think mentioning Archenland and Calormen in LWW would explain a lot. I'm assuming the Narnians got all their food from those countries since they couldn't grow crops. Having other countries with human occupants confuses the White Witch's reaction to the children through. If there were humans just one country over, she shouldn't be so surprised to see them. Maybe Lewis planned to revise that somehow, perhaps by making the prophesy be specifically about children from another world.

I would also remove the "talking down to children" that is present in LWW and not in any of the other books, such as "if I did [describe the Witch's followers], the grown-ups might not let you read this book". That made me squirm when I first read LWW when I was about 6 or 7.

Huh, I had a different take-away from that line. I always assumed Lewis included it because he knew his reader's imaginations would fill in what they feared or loathed most. The shark wasn't shown much in "Jaws" because it was corny looking, but that made the movie much scarier than it would have been if the shark was in every shot.

I find a brief line in "The Last Battle" really interesting. After Jewel has been rescued and Poggin joins the group, Jewel tells his story in one paragraph. The last sentence reads "He didn't know what had happened to the Lamb." As far as we the readers know, nothing at all HAS happened to the lamb. The Ape yells at him and then he isn't mentioned again until Jewel's cryptic line. I have to wonder if that's an editing error and Lewis first wrote that the Lamb was also imprisoned. Perhaps the scene was cut for some reason after that and Lewis missed this little line. It's probably small errors like this that Lewis would have polished up.