Is it permissible to account a sum of zakat that was intended as charity and then its intention changed to zakat when given to the poor, or to account a sum of zakat that will be deducted from the salary in a later month, knowing that it was intended as charity?

Intention (niyyah) is a condition for the validity of zakat. If a Muslim gives charity with their wealth without the intention of zakat, it will not suffice as zakat. The intention must accompany the act of giving out zakat or precede it by a short time. Therefore, if someone gives out money with the intention of charity, they are not permitted to count it as zakat afterwards. However, if they intended charity, then changed their intention to zakat at the time of payment or shortly before it, this is permissible, because charity is not made binding by intention alone. As for the sick person, their illness does not permit them to receive zakat unless they fall under the categories of those entitled to it.