Karl borrowed P10,000 from Grace. It was agreed that Karl could pay P10,000 or deliver the latest pair of black Adidas Ultraboosts on December 31. On December 22, Karl informed Grace that he would deliver a pair of Ultraboosts. Can Karl still change his mind considering that he was given the right of choice? (must have legal basis and reference to the articles on Obligations in the Civil Code as much as possible)