And that is second hand private key indeed. Why on earth will I ever want to buy a private key from someone when all it takes is just a split of minutes to get it transferred to my wallet where I control everything ? Just for the knowledge, so as to clear your assumptions for next time, private keys cannot be changed, and if you find yourself in the position of wanting to buy private key, then it is more like you sharing the asset with another person you are buying it from with both of you having full control of it and by then, it would be who is the first to move it out ? At that point, you do not want to be the last.