Currently this works only for Getting or Updating the entire Project. Anyway you can GET all model definition by simple API call. See the documentation:
http://docs.gooddatadrafts.apiary.io/
There is a GET request which is asynchronous. You can build some logic on the top of that on your end. You can get all models, store per datasets information, but at the end you need to POST the "final version" and all updates will be applied.
Let me know if I can help you with anything!
Regards,
JT