Ethical considerations aside, as other posters have noted it is probably held in with animal glue, and should easily come away with heat or steam. The pieces are very small so they might even be be bone, rather than ivory.
For a project I worked on, a few years back, I looked into ivory alternatives, and there were quit a few. Tagua nut (vegetable ivory) , being one. I made quite a convincing, cast polyester resin for my project , but some sort of plastic veneer/ piano key top, would probably be easier or you to work on, and apply.