Is it permissible to change or cancel a vow before the baccalaureate exam, given that the vow is to fast a month if a grade of 16 is achieved?

Whoever vows obedience to Allah, it is obligatory upon him to fulfill it, as the Prophet, may Allah’s prayers and peace be upon him, said: “Whoever vows to obey Allah, let him obey Him.” Therefore, it is not permissible to change or invalidate a vow; rather, it must be fulfilled if the condition upon which it is suspended is met, otherwise it is not obligatory.