We'll create fresh WordPress site with Published Posts Locked URL installed. You have 20 minutes to test the plugin after that site we'll be deleted.
In WordPress you can change the post name, which will impact its final URL and probably mess up the SEO on that article, since search engines will think both the previous and the new URL are different contents. You could fix this arranging some 301 redirects, but with this plugin active you just won’t be able to change that post name – hence its URL – unless the post is still in draft mode.