On Windows, renaming the file makes appears to work, and the interface will indeed show "foo.cbz". But what it actually does is rename the file "foo.cbz.zip". The actual extension remains entirely hidden and untouchable as long as the global option to hide extensions is turned on.
On the Mac, changing the name to "foo.cbz" will prompt a warning that you might cause the file to open in a different application, and IIRC presents the options of naming it "foo.cbz.zip" or "foo.cbz".
Neither approach is perfect, but I think what this illustrates is the difference between walling off complexity and just hiding it. We see the same difference with Chrome, as hiding http:// is just visual, but the altered way of copying URLs to the clipboard is actually blocking the user's access to that complexity.