Yesterday I wrote yet another article (I don’t mean that this is my second or third article, I mean that there are plenty of such articles over internet) about writing an OpenFL extension.
Maybe it can be useful for someone: http://blog.zame-dev.org/openfl-extension-in-10-steps/
P. S. It is not just tutorial, but ready-to-use extension to change screen orientation, feel free to use it.