I've never rewritten subject matter, exactly; I think chapters are defined by what they're about, so if I were to regret a chapter's primary focus then I would likely just delete it (provided doing so would be structurally feasible).
In stories that heavily depend on plot and a tight, accurate chain of cause and effect, I have 'retconned' tiny details in early chapters that the average reader would never pick up on but would slightly contradict an important fact in a later chapter. The actual impact of doing so is very small (or so I hope), only noticeable if someone were to collect every detail in every throwaway comment and casual description in the hundred-and-something-thousand-word story to check for such errors. I would never make a significant change for the sake of continuity because I know there are at least a few readers keeping up with every instalment, and if it's information they might have retained then they'll be confused.
In stories that are more focused on branching, particularly Game Mode stories, then I don't see any problem with cleaning up prose that doesn't contribute to the reader's impressions of the characters, plot or world. Even then, I have twice made significant changes to a part of such a story when I found it highly doubtful that anyone would be reading new content without also reading my those changes (once when the story was very short and untouched for nearly a year - although someone did notice and mention it - and another when the changes still didn't actually matter later on, just for the succeeding few chapters).