What is the ruling on attempting to surgically reduce the size of the nose and then feeling regret, considering this to be a change in God's creation? And is it permissible to supplicate for the nose to return to its natural shape?

It is permissible to supplicate for the removal of harm resulting from cosmetic surgeries. However, lack of a perceived immediate response does not mean the supplication has not been answered. The supplicant may be granted what he asked for, or an equivalent evil may be averted from him, as long as he does not supplicate for sin or the severance of kinship ties.