Can the intention of an ongoing charity (ṣadaqah jāriyah) placed in the mosque be changed from a person to his deceased grandfather, merely by a new intention, or is the first intention the fundamental one?

Placing a water cooler in a mosque is considered an ongoing charity (Sadaqa Jariyah) and an endowment (Waqf) by the majority of scholars, even if the intention of endowment was not verbally expressed. The act itself, such as building a mosque or preparing land for a cemetery with general permission, is considered an endowment. An endowment becomes valid through an act that customarily indicates it, like building a mosque and allowing people to pray in it. It is permissible to dedicate the reward of an ongoing charity to one's grandfather, for whoever performs a good deed owns its reward and may bestow it upon whomever he wishes.