I don't know the answer to your question but like you would like to find out. I also have a very low mileage (34,500) '13. I suggest you look at the emissions fix warranty booklet very carefully about what it says re: tuning the car, and not just trust what someone posts here. You are on the hook if VW denies a warranty claim notwithstanding what anyone posts on here. Also, in your case that extended warranty will expire I believe 10 years after the original in-service date (some time in 2022). That's not far off.
I frankly would not chance voiding the warranty for the sake of the DSG tune unless you have really clear guidance that the warranty will not be affected. In my car, the DSG is really smooth and has lightning fast shifts; I personally feel no need to improve or smooth out the transmission at this point.
By the way, at 40K you are actually due for service of the transmission. Have you done that?
I am only going to consider tuning my car after the extended warranty expires. Too many things can and do go wrong with this car, especially the various components associated with the emissions system