Is it permissible for a person who donated charity on behalf of a deceased individual to then include himself in the intention for the reward?

It is permissible for the giver of charity to include others in his intention when giving the charity, as it was narrated that the Prophet (peace and blessings be upon him) sacrificed a ram and said: "O Allah, accept this from Muhammad and the family of Muhammad, and from the Ummah of Muhammad." It is better for one giving voluntary charity to intend it for all believing men and women, so that it reaches them and his reward is not diminished in any way.

Any act of worship performed by a Muslim, the reward of which he dedicates to a deceased Muslim, will benefit the deceased by Allah's permission, such as charity, supplication, and seeking forgiveness. As for charity after it has been given, it counts for the one for whom it was intended, and the giver of charity is also rewarded for his intention.