There’s a piece of writing advice that goes around and around, and it says: “Write first, edit later.”
What this means, is that you should concentrate on finishing the story before you start tinkering with it, or you’ll never finish. And on the whole, it’s sound advice. You need to get the first draft finished before you can really see the shape of the thing, so that early chapter you spent so long revising might not even be needed anymore.
However, I’m not one for prescriptive advice. You can do it that way, or you can do what I do, which is sort of halfway between the two extremes.
I try to get my first draft finished before any major changes, but if there’s something huge that affects the rest of the book, I’ll go back and change it there and then. Also, if I’m finding it hard to get going, I might go back and edit some earlier scenes to ease myself back into the flow of the story.
Using this approach, I tend to produce fairly clean first drafts. They may need some structural edits, but they’re not a complete mess.