The official guide is here: http://chyoa.com/story/chyoo-guide/cover It doesn't have a list of rules, but it certainly helps. I don't know of any official rules list. Plagiarism is common sense, just don't. As a rule of thumb in general, if it feels wrong, it most likely is.
here are the official guidelines: http://chyoa.com/guidelines The link is on the right side below "About Chyoo" I think, that list isn't "complete" and should be revised someday. Especially to separate rules from guidelines.
