Hi Rik,
I use a lot of ivory (mostly fossil) in my work, and you should think of it as identical to a dense and very brittle wood. It swells and contracts with moisture, it has grain, it absorbs liquids, it cracks and discolors with age, it has soft spots and hard spots, it will craze if it gets hot (like in polishing). If you are going to use through pins for slab handles, I wouldn't peen them in place (you'll crack the ivory), just epoxy them. Treat ivory like a delicate lady. Any user who is mistreating an ivory handled knife deserves what they will get, anyway.
I often use a wood oil finish (like Watco natural/clear, or plain thinned linseed oil 50/50 mix) on my wood and ivory pieces, and usually don't see problems in the ivory portions. Oil will change the ivory surface appearance, just like it will for wood. I don't think I would try for any really significant oil or resin penetration like in stabilizing.
My two cents.