I have done this type of re-booking process several times online, including as recently as last February. I do use 2 different pc's and log in to my account on both devices. I cancel the old reservation on one device while holding the new reservation open on the other device (you go to the point where they want you to select to which contract to use). After you cancel the old reservation you just refresh the device with the reservation you want and the points from the cancelled reservation are back in the account to use. I am fortunate that I haven't had any problems...yet, although I always worry the internet will crash or something. It does save time, though, as you don't have to wait for MS to open at 9am (and risk losing what you want) if you want to change your reservation and use points you have already used to book the old reservation.