I have changed no portion of the story
Most modern commentators would dispute this statement strongly, taking exception both stylistically and substantively, and tending to see the 1831 edition as truly a reconception of the 1818 edition rather than the tidying-up suggested here. But it is not entirely easy to focus categorically on the differences between the texts. Some political innuendos of moment in 1818, for instance, were no longer relevant to the changed climate in the year before the Great Reform Bill, but that does not mean that others—for instance, the curious intrusion of imperialism into the plot (see I:6:14 and note)—have not taken their place. Mary Shelley did greatly rewrite the first chapter of 1818 breaking it into two separate chapters in 1831. She similarly reworked the opening chapter of Volume 2. Throughout her revision she endeavors to flesh out her characters rather than merely to add descriptive elements to the novel. In this regard, her most extensive elaboration is in making Victor's account of his life from the very beginning subtly reflect the paranoid mental condition to which experience has reduced him.