Unless buying it works. The first thing that came to mind was buying the identification papers of a dead soldier and using them. Not legally appropriate, but certainly practical in a time of chaos, warfare and death. If you pull it off, after 2 or 3 generations it becomes a families reality. It would hardly be a rare occurrence given the number of times humans have made war on each other.
Rebellion is treason...unless you win. I think taking a fake identity is much the same.
