Is it permissible to change the intention of a vow (nazr) designated for a specific poor family and give it instead to another family that is poorer and includes a cancer patient?

A Muslim must fulfill his vow to the entity he vowed to, and in the manner he vowed it, because Allah Almighty says: "And let them fulfill their vows." Therefore, it is not permissible to divert the vowed offering to another entity, even if it is more in need. However, there is no objection to helping the family or the sick with money other than the vowed offering, if it is available; otherwise, there is no sin.