Is it permissible to psychologically harm one's wife for the purpose of gaining custody of the child, especially given that she does not adhere to the teachings of Islam after converting?

The majority of scholars hold that a disbelieving woman has no right to custody of a Muslim child. If the mother persists in her apostasy, then stratagems must be employed to take the child from her. If this is not possible, the father should strive to visit, raise, and teach the child whenever he meets him.

As for the mentioned action, if what is meant by it is magic, then it is not permissible to use stratagems by committing disbelief or injustice, nor to request such actions from sorcerers. The Prophet, peace and blessings be upon him, said: "He is not one of us who practices magic or for whom magic is practiced," and "Whoever goes to a soothsayer or a diviner and believes what he says has disbelieved in what was revealed to Muhammad, peace and blessings be upon him."