I believe that you just have to change the orifices, this requires a burner mechanic with a special licenses. we used to install all sorts of natural gas equipment years before the gas came down the street. and then when it did arrive we would do a switch over.
Propane = LP
Natural gas = NG
Many devices have a kit available to convert between the two options. Sometimes it is just new orifices. sometimes it also involves a change to the built in regulator.