Is it permissible for someone who has designated money for a specific charitable act to change their intention and spend it on another charitable act, such as an endowment, given that the money is deducted monthly from their salary and was collected with this intention?

It is permissible for the owner to change their intention regarding the expenditure of their wealth and to spend it on any cause they wish, as long as the wealth remains in their possession and has not yet been disposed of. Indeed, it is recommended for them to spend it on a more virtuous cause if they come to know of one. Endowments (waqf) are considered among the recommended deeds, as they are a continuous charity (sadaqah jariyah) whose reward persists for the individual after their death.