Can I replace the pilot light unit on my propane furnace or replace it with an eletric spark starter?

They make a kit to convert a standing pilot furnace to an intermittent spark ignition system. I recommend you have a qualified technician do the work. If your furnace has a standing pilot, that means you have an older furnace. Why not consider replacing the furnace? Rather than dumping money into an old one put the money toward a new one. New furnaces come standard with electronic ignition. They are also more energy efficient, are safer, and come with a warranty.