Is it permissible this year to send a sum of money that used to be given out annually as food for orphans to a children's cancer hospital, knowing that it was a commitment and not a vow?

The questioner did not make a covenant with Allah the Almighty. Rather, he intended in his heart to donate money each year according to his ability, and he did not specify it for a particular entity. Therefore, there is no harm upon him in diversifying the expenditures of this money, so he may disburse it to charitable organizations, the poor and orphans, or for the treatment of the sick or the teaching of knowledge, as he deems appropriate.