You don’t need to escape (add a backslash before) the dot. The problem, I suspect, is that the items that aren’t being updated are pages, not posts. Page permalinks behave slightly differently and I suspect you’ll need a custom plugin to add .html to the end of a page.
Hi Otto42. I tried that. When you attempt to add .html to the slug, WordPress automatically removes the period. So the slug then reads “pagenamehtml” instead of “pagename.html”. I’ve tried to escape the period with a backslash (pagename\.html) to no avail. Same result. I’ve even tried a double dot (pagename..html) also to no avail. Same result. Always just comes back as “pagenamehtml”. But thank you for the suggestion.