It is possible but you have to install the upgrade patch and to open the files manually. Also it is possible to make your tomtom think it is another (expensive ) model by altering the tomtom software hack. I have a One Xl and it thinks it is an GO640.
I'm missing something then if you want your xl to think it's a go series. What is the advantage or advantages in doing this? How hard is it to do? I'm guessing it voids the warranty as well.