At what point does an author's right to revise their own work conflict with a reader's right to the book they actually purchased?

Do you think authors should be able to make substantial, retroactive changes to a published book--including removing or rewriting entire scenes--without releasing or clearly marketing the revision as a new edition? And should those changes be pushed to copies readers have already purchased?

I'm asking because I've seen this come up with a popular romantasy series where the author is retroactively removing all of the sex scenes and changing them to fade-to-black. It's sparked a lot of discussion about authors' rights, readers' rights, ownership, and whether a published book is ever really "finished."

I'm deliberately not asking about this specific author or situation, which is why I'm posting this in Club. I'm more interested in the broader question: Where do you draw the line? Are authors free to change anything they want after publication because it's their work, or does a reader have some reasonable expectation that the version they purchased will remain the version they purchased?

And if you think authors should be able to make these kinds of changes, what would you consider significant enough to warrant labeling or selling the revision as a separate edition?