The static pressure in my ductwork is 0.5 H2O supplied by a 500 cfm fan but I need an additional 1 H2O with no additional cfm will an additional fan with a 500 cfm rating work?

Okay, to get the static pressure in your duct to from 0.5" water gauge (w.g.) to 1.5"w.g., you could add another fan in series. Or, depending on your existing fan and motor size, you may be able to speed up your current fan to the pressure value desired. Additional airflow would be dampered down.