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.
catholicculture.org/culture/library/dictionary/index.cfm?id=37098
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