I know this is very common among Mahayanas, specialy in Tibet where they search for their old teachers (Lamas) all call them Rinpoche.
Is this also a practice in Theravada Buddhism?
Teachers consciously reincarnate because they took Bodhisattva vow. They promised they will be taking rebirth until they liberate all sentient beings. Because in Theravada one typically does not take the vow, tulkus are not searched for.
One can also argue that in order to be consciously reborn, one should master advanced tantric practices from the level of Mahayana/Vajrayana. One of such practices is Phowa, also called 'the practice of conscious dying' or 'transference of consciousness at the time of death'. The idea is that the practitioner learns how to work with energies at the moment of dying and after leaving the body instead of being at the mercy of their karma, they can consciously choose the next rebirth.