Maybe he changed the character to Guiseppe Mariposa because the novel is set in 1934, and Salvatore Maranzano is a real historical figure in the history of organized crime, and he died in 1931. Luciano and Lansky set up Maranzano after they learned that he had hired Mad Dog Coll to murder Luciano and Vito Genovese. In The Godfather, Puzo has Maranzano still alive in 1933, two years after he'd been killed. Maybe Falco figured better to avoid the historical inaccuracy and come up with a different character name.