-webkit-user-modify: read-only | read-write | read-write-plaintext-only;
This allows for 3 different values: - read-only - This is the default and will not allow the user to edit the element
-moz-user-modify: read-only | read-write | write-only
This also allows three values but they are slightly different. - read-only - This is the default you can read the content but not write the content.
View the demo to see how this will work Demo
The way this can be used in a CMS page is for admin user to preview a page of their content on the real page and not in a text editor. Then allow the admin user to click on a paragraph, you can then add the -user-modify CSS property to the clicked element. When this element loses focus you can grab the changed content and use AJAX to update the database with the new content.