Thank you for your help.
I've put the 'quiz_edited' folder back in the /mod folder alongside 'quiz'.
Also I added 'quiz_edited' to the 'modules' table. But when I go to Administration / Plugins / Activity modules / Mange activity modules, it shows error like the is no $string['modulename'] in /lang/en/quiz_edited.php.. But I checked - such a string exists.. Why Moodle doesn't recognize it?
Also now, when trying to go to /mod/quiz_edited/view.php?id=777, I get this:
Invalid component used in plugin_supports():mod_quiz_edited
I know it looks like I am doing it the wrong way, but how to do the basics:
What should be done step-by-step to make Moodle system recognize my 'quiz_edited' folder, which is at 90% similar to the original 'quiz' folder?
Thanks all helpers!