I love ebooks. I can publish, revise, republish, revise... You mention early parts of a book. It gets more complicated with early parts of a series. I have changed characters in many ways. Bad guys become less bad - or more. Good guys change alliances. Eight books in, I may flip a character totally. As for readers, those who read a version a couple years ago are never going to know. The newer readers will read a better version.
But back to your original question - should you revise early chapters while still writing the book? NO. Keep going. Finish the book. By the end, you will have found far more things to revise. And you may be revising from a completely different perspective. FINISH THE BOOK.