Hello Tim,
Good question.
I think you understand that you can edit post after publishing
Ido it all the times with blogs

Yeah, you can actually edit any of the posts you've published on your blog again and again. No penalty for that at all!

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When I update a post, before I click update, I usually change the publish date, and then go to google webmasters and ask them to crawl it again.

Yes, you can do that in WordPress Backoffice. Just update some important or relevant point because Google might have ranked certain of your keywords or phrase in your content.

You can edit them, I regularly update my reviews with more up to date content (for example I am just writing some more information on the site comments platform for my WA review) so i will be adding this when it is ready.
If your content isn't converting, then you can added more notes to it. I wouldn't recommend changing your title or keywords.
But if you need to edit it to make it more relevant to the audience, go for it.
I have rewritten a number of my early articles. Your writing improves as you progress.

Yes, you do that at WordPress.
Log in into your website and then click on posts, and you can edit any post/page you want :)

The Googlebot scours the web (a huge space) constantly for new content and will index your new posts when it visits your site. Alternately, you can submit a sitemap to Google to have your site and all its current content indexed, as well as using the 'fetch as Google' feature of Search Console.