Is it permissible to exchange an Udhiyah designated for the deceased for another Udhiyah of better quality, and to designate the first Udhiyah for the sister?

It is permissible for someone who has designated animals for sacrifice on behalf of individuals, and these animals have not yet been taken possession of, to substitute an animal designated for one person with another. This is because the substitution occurs within his own property, and the animals do not cease to be sacrificial. However, if the animal has been gifted and taken possession of, it is not permissible to revoke the gift, due to the impermissibility of revoking a gift. If it has become the property of the donee, he is prevented from substituting it if it has been specifically designated as a sacrifice by utterance, "The one who revokes his gift is like a dog that vomits and then returns to its vomit."