Of course it will be able to do that.
You are already doing that in part, now all you need to do is provide options to a restricted interface so that he can choose how to update.
The simplest interface for this, IMO would be to read the textfile, display it in a textarea, then when the form is submitted, write the contents of the textarea into the textfile.
Of course for safety you might want to provide an automatic backup file or something.
drew010, please read the question in context before answering.