Is it valid for the one who gave an ongoing charity (sadaqah jariyah), intending it for a deceased person, to then intend to include himself in its reward?

The intention to share the reward of charity is not valid after the act of charity has been completed and the intention was firmly set that the reward is not to be shared. This is because the time for intention is at the beginning of acts of worship. If a person gives charity and dedicates its reward to a living or deceased person, it is not permissible for him to include himself in its reward after it has passed. However, the one who dedicates the reward of charity will receive the reward for beneficence and aiding in good.