Can a New Yorker go to another state to purchase it as long as your registered?

It will depend on which state you go to. A helpful article with information may be found by visiting https://www.leafly.com/news/cannabis-101/which-us-states-accept-out-of-state-medical-marijuana-authorizati

I did some reasearch on this, and you have to be registered in the state you are purchasing it. You also can't take it to a state where it is illegal and it is federal offense to fly with it.