Can you use a program such as EasyGPS (Google) to unload them from one
unit and load them into the other via a portable computer?

Unfortunately no! I already use a similar program as well as some
home-made programs, but all of them work with PORTABLE GPSs. GNS530 is a
panel mount GPS and doesn't have the standard Garmin interface, used
by ant commercial program like EasyGPS, GarTrip, etc.

GNS430 has 4 serial ports, but the software interface (protocol) seems
not documented.