How does this look to you???
I wouldn't put it in the document, as then it's disruptive to new readers (and the majority of readers will read it long after you've finished posting). Instead, I'd put it in your blog. Face it, the majority of readers will only read your story once, and won't really care about minor (non-plot centric) changes. You need to focus on them first. By posting the changes or details to the blog, then those who are interested can follow your progress and provide feedback about it.
Another alternative, when you submit the chapter, as the Administrator in the submission process to post it as chapter 1A or 1.5 (if they can). That will flag it as a new chapter, but get it into the correct numeric sequence without disturbing the flow of the story.
Or he can post it as a rewrite of the story using the wording "Version 2" or something.
The reason why I advise against deleting and reposting a story, is that the majority of readers are impatient. They don't care about works "in progress", they simply want to read something. If they read a story, then start a new story, only to discover it's the old one, reworked, they're likely to abandon you as an author, and never come back.
The number of readers who want to see both versions is incredibly small, so reposting a new version (as a separate story) will disappoint more readers than it was please. It's a no-win situation!
Aerosick, another alternative is to post it as a separate short story. Simply write a one chapter story about that one even in your life, create a universe incorporating both stories, and let the earlier events stand on their own. That way, you'll always know how readers reacted to the new chapters, rather than guessing based on score variations at the time of posting.