Manufacturers Statement of Origin = MSO
I wouldn’t use a KX as an on road bike (or ANY high power 2 stroke for that matter) but thats just me. I would suggest looking at something like a KTM 690 Enduro thats a legit on/off road bike from the factory.
DMV could register the previously registered bike to you, however, in some instances (not sure about NYS) there have been title revocations done for this exact thing. Again, look into getting a legit on/off road bike and not an amateur conversion.