Assignment

Hello,
I am just curious about a way to have assignments password protected. My goal is to have an assignment that only one user will be allowed to modify and edit. So I would have a global course with private assignments for certain people. My intention in this I wish to have active stories written by students, I then append and correct the errors as we go along. In the end there is a short story, which could be published to the class at the end of a course. Is there any experience out there in something like this? Has this been done before? What are the best tips and tricks what to sue and not? Any information is appreciated.
Kind regards,
Corey