Well, I decided to take on something slightly less ambitious, and after much trial and error, I have successfully written a lua plug-in which will set Nav 1 to the ILS frequency of the desired runway using the arrival airport code gleaned from the active flight plan, and a runway number submited by the user through ipc.ask. As the .PLN files do not contain frequencies, I made an ILS frequency database by modifying a csv file called "runways", which I found floating around my FSX folder. Perhaps Radar Contact put it there or something? In any case, it works, and I see no reason why the same principles can't be put to work to create a plug-in to set the nav radios to successive VOR waypoints, as was my original design.
Thank you very much for your help! Without it I might still be barking up the wrong tree.
Farley