If you change your sslsubstrees in site.ini after they've been defined, they are simply ignored.

Steps to reproduce

Setup

1. Open terminal window
2. Add the following to you site.ini.append.php

   [SSLZoneSettings]
   # Enable/disable the SSL zones functionality.
   SSLZones=enabled
   # Content subtrees we must use SSL for.
   # (currently, only content/view and content/edit respect this setting)
   #
   # Examples:
   # SSLSubtrees[]=/news
   # SSLSubtrees[]=/polls
   SSLSubtrees[]=/sports
   

3. Clear the caches

   $ php bin/php/ezcache.php --clear-all --purge
   

4. Add two folder
   1. Login into admin interface, using admin account
   2. Click on "Content structure" from the top menu
   3. Click on "Create new" button
   4. Choose "Folder" from the drop down list
   5. In the "Name (required):" fill in "News"
   6. Click on "Send for publishing" button
   7. Click on "Create new" button
   8. Choose "Folder" from the drop down list
   9. In the "Name (required):" fill in "Sports"
   10. Click on "Send for publishing" button
5. Access you site frontend
   1. Click on "News" folder
   2. Verify that you're still in http mode
   3. Click on "Sports" folder
   4. Verify that you've changed to https mode
6. Change SSLSubtrees
   1. Change the SSLSubress in site.ini.append.php to News

      [SSLZoneSettings]
      # Enable/disable the SSL zones functionality.
      SSLZones=enabled
      # Content subtrees we must use SSL for.
      # (currently, only content/view and content/edit respect this setting)
      #
      # Examples:
      # SSLSubtrees[]=/news
      # SSLSubtrees[]=/polls
      SSLSubtrees[]=/news
      

   2. Clear the caches

      $ php bin/php/ezcache.php --clear-all --purge
      

   3. Access you site frontend
      1. Click on "News" folder
      2. Verify that you're still in http mode
      3. Click on "Sports" folder
      4. Verify that you've changed to https mode