It is possible to use the Garmin 430/530 to load a takeoff alternate approach in case of an emergency shortly after takeoff. This takeoff alternate need note be the same as either your departure or your destination airport.
Supose you are flying from A to B and you want C to be your takeoff alternate. After loading your flight plan in the usual maner, press:
PROC
Select Approach Press CLR (this is the most non-intuitive step)
Turn Large right knob to the left until airport identifier is highlighted
Change the identifier to the airport you wish for your takeoff alternate
Select the desired approach