what I do is use this to save it:
https://chromewebstore.google.com/detail/form-saver/gcghnngjnejahhomknolenehfhfbijjh?hl=en
and if I want to edit a hidden post, I:
1. find the post it's on
2. duplicate the tab
3. go back to the first tab and unhide it and then click "edit"
4. go back to the second tab and re-hide it
5. now I have the editor open in the first tab but nobody else can see the post
6. when I'm done, I go back to the second tab, unhide it, and then go back the the first and press "save changes"
Note that if you don't unhide it in the second tab, when you click "save changes" it will not apply the changes due to the post being hidden, but if you have the form saver extension I linked to earlier, it'll save your answer, which is nice.