AFAIK, you can not apply that in Spanish, You should use the masculine plural gender to refer to both genders, or when the gender of the people is unknown.

There are exceptions to the rule, like the one above (Zapatistas) or some professions like "doctores" or "jueces", but they are exception not the rule. There are also many words that dont have a feminine plural, i.e "las soldados", "las jueces", etc