The text of The Merchant of Venice indicates that Antonio doesn't change at all through the course of the play. In this regard, the literary element of character change would be antithetically presented in a staunchly unchanging character who holds fast to errors despite drastic situations that call for a change of character. One instance of Antonio's errors, which are derived from his character traits, is the fact that he seems to actually lie in the opening scene when he tells Salarino and Salanio that his wealth is not all in one venture nor dependent upon the financial success of that one year. His dishonest remarks to Salarino and Salario are revealed in his conversation with Bassanio in which he says that "all my fortunes are at sea; / Neither have I money nor commodity / To raise a present sum."
Another instance of Antonio's errors is what is revealed about his behavior while Bassanio and he are in negotiation for a loan with Shylock, who reveals that Antonio has hurled names at Shylock and spit on him and that he "did void [his] rheum upon [Shylock's] beard" and " foot [Shylock] as [he would] spurn a stranger cur." Antonio doesn't deny that he took such base actions, in fact, he confirms it: "I am as like to call thee so again, / To spit on thee again, to spurn thee too."
During the conclusion of the trail, when Shylock's punishment is being decided, Antonio successfully contributes to Shylock's punishment by continuing to persecute and impose his will upon Shylock and requiring, among other things, that Shylock convert to Christianity. Later, this same manipulative streak is displayed when he requires that Bassanio give Portia's ring to the lawyer/Portia against his will, as he swore to never part with it. He even speaks for Bessanio by pledging his own life again and saying that Bessanio swears to never break another oath given to Portia.
The most telling point that indicates there is no change in Antonio is that at the close of the play, he still thinks of Shylock as a despicable Jew and doesn't even entertain an idea that recognizes Shylock as a human, and one who has been seriously mistreated, so seriously as to drive him to strike a bargain for a pound of flesh.