A friend paid some charity for a sick person, and wants to give Zakah Al-mal (Zakah). Is it possible to change his mind and consider the charity as a part of the Zakah?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. It is unlawful for your brother to consider this alms as part of his Zakah because of the lack of Zakah intention at the time of giving it. Indeed, Zakah is not valid unless there is an intention that what is being given is the obligatory Zakah. The evidence is the known Hadith that the Prophet (Sallallahu Alaihi wa Sallam) said: "Deeds depend on the intention behind them. Each person will be given according to his intention" . Allah knows best.