I think that it is also a personal choice.. Like look at the lives of Saint Faustina, Saint Therese.. they themselves wanted to suffer for the sake of the world. And I they did this through constant communication with God and sometimes via visions / revelations where Jesus actually asks if they want to be a victim soul or not.
Victim Soul: A person specially chosen by God to suffer more than most people during life, and who generously accepts
the suffering in union with the Savior and after the example of Christ's own Passion and Death. The motive of a victim soul is a great love of God and the desire to make reparation for the sins of mankind.
So yes.. I would say that being a victim soul would also be a personal choice, although God may ask them.. but the choice is ultimately up to the soul