Please read this post and see note 7. How to get help on the Dynamo forums
I am only going to give you minimal information:
You need to look into the revit sdk, but do note that the api for this only got added into revit 2017.
I have coded something that was all in python that gets/sets this information but it was all python orientated(below video of it running) I currently have no plan on releasing this script.