When one joins the Dominican Order, it is the Provincial Superior who assigns you to live in a particular community of the Order.
It can happen for reasons of study or of apostolic work that you may have to live elsewhere for a time, but even then you are considered to be a member of a particular Dominican community, and that community will show interest in your welfare. At the moment novices are assigned to our Johannesburg Priory, students studying at the seminary are assigned to live in our Pietermaritzburg Priory, priests working in parishes or in other tasks are assigned to the nearest Dominican house.
Postulants are not yet members of the Order, and so are not assigned in this way. They are merely sent to live with one or two Dominicans in a special postulants’ community. They only get assigned once they begin their novitiate.