At first, i checked all scripts in use, and make sure that they can be loaded over HTTPS, so i don't get mixed content warning from browsers, when protected page contains some unprotected elements. Also, i got this warning because my old code for E-Mail subscription from Feedburner service contains two HTTP references. I took new code (it refers to HTTPS), and problem was solved. With all blog photos and graphics i have no problems, thanks to Flickr, who switched to HTTPS long ago. Although, i checked posts with old Flickr embed codes (taken before Flickr HTTPS support was rolled out), and get new codes for all these images.
But then, i need to change all internal links in all posts and pages from absolute to relative form:
Then, clicking a link on protected page will load protected, and click on standard HTTP page will load standard. This was really hard work, because my blog have almost two hundred posts and static pages, with hundreds of internal links. As side effect, i checked also all outgoing links: updated many of them to HTTPS versions (for sites that supports it), and removed several dead links (or updated them to proper versions, if they can be retrieved).
So, if you will go to any protected page, you'll surf protected version of blog:
...and standard HTTP pages are fully functional, too: