There is very little doubt that the Chinese were around America at least 70 years before Columbus. One has to wonder if the change in leadership back in China....mandating no travel and closing off the country...had kept the course instead....China would have been the most dominate country on Earth by the 1600s. The use and further development of new technology is obvious. The world today would be a much different place had the no closure occurred.
As for the Chinese who landed in America. One must wonder if they brought disease...as did the Spaniards...and if the Indians eventually decided the only good Chinese were dead Chinese. There is little written about gold-obcessed Chinese explorers...unlike the Spaniards.
As for how history changes once this is proven....and I think we are talking about just six months of research to prove DNA on this item...history is a ever-changing thing. The Vikings and their travel have been a constant argument for years....and most people are finally willing to accept that Vikings did come to America. We will likely see other developments which challenge our high school text books.
100% of scholars agree that the Vikings were living on the North American coast in at least one long term settlement.
Like I said if any people got to the Americans before 1492 AD they had no idea where they were, were lucky to get back alive and once home had no idea how to retrace their voayge.
I think the issue here is what historians call "diffusion" in other words contacts maintained long enough with the Americas and the old world for culture and technology to be diffused back and forth. This I think never happened.