Surname reservations are not going to be locked anytime soon, so you don't have to lock one in right away if you don't want to.
Once you lock it in though it is pretty solidly locked in. Surname change tokens are going to be a thing prior to launch, but we don't have a day yet.
You will have to use your surname reservation during exposition (to my knowledge). If you miss this window then you will only start the game as someone with a predetermined name based on your family, or no surname at all.
Just get your friend invested in your surname sometime between now and launch and you will be alright!