I would assume that this idea was dropped due to complications of the mechanism. Because how would that work with market? Wouldn't had to be a new sprite over there too or cyclopedia(because it would be only cosmetic change means you can still sell it right) ? But then, that would contradict the "surprise" effect. Considering that with that update we had few items which can be enchanted, it could have work like enchanted items- but again, it is bit troublesome to remove option of trading the item only for cosmetic effect. Now, I would say it will got to do with colour of the orb or shinning effect around it as we receive following message when returning the amulet "The orb inside the amulet disappears in a gentle glow the very moment you place it on the small pedestal." "A small note reveals itself in its place.".
Frankly, It would be better that instead of cosmetic change, it would give back Cobra Amulet properties to all Note About two Souls (death protection etc).
I guess the easiest would be to change look of the altar instead of all amulets on server.
Perhaps none yet delivered right amount and sprite is to be yet uploaded to the client ;-)