It is not actually true that surnames ending in “ez” are of Jewish origin, although many people of Jewish origin used those surnames. Asturian patronymics ended in “ez” (Gallego and Portuguese patronymics, on the other hand, ended in “es”) with Rodrigo, the son of Gonzalo Pérez, having the name “Rodrigo González,” Sancho, the son of Rodrigo González, having the name “Sancho Rodríguez,” and Pedro, the son of Sancho Rodríguez, having the name “Pedro Sánchez.” When Jews in Spain had to adopt surnames, many just followed the Asturian custom in order to fit in, but Jews were a minority of those who bore them; the Spanish surnames with the highest percentage of Jewish bearers likely were the more overtly Catholic-sounding ones, like San Miguel or “De Jesús,” which were often selected by conversos precisely as an attempt to have their Catholicism not be questioned.
This new law presumably applies to Spanish Jews who weren’t conversos, but who left Spain in the 15th century in order to keep practicing their faith, so I don’t think that any Hernándezes ir Pérezes or Gutiérrezes need apply irrespective of their genealogy.
That explains a lot about my last name, which is related not to a personal name, but the the name of a crop, followed by ES.
Gracias!