Everything is possible. The "order change" will cost you an additional $35.00. Randall does not supply ivory or fine silver. You would have to purchase those items on your own.
Have you already paid for the knife in full? If so, the money applied towards the nickel silver, metal spacers, butt cap and stag would be credited towards the installation of your silver and ivory. Those labor charges, plus the $35 order change would probably eat up all that you had paid...and then some. The ivory install and order change adds up to $100 alone. I don't know what the shop charges for installing silver, as I don't do that much of it. Hope this helps.
Best, Capt. Chris