I've installed and enlarged position dots, which is easy (brad point drill bits and precut pearl dots). I've also done rectangular Gibson style ones, which are more difficult to to, thanks to the corners (I did mine freehand with a Dremel and a scalpel). You need to set up a jig so you can keep the bottom or the rout flat - it can't follow the fingerboard radius.
Anything else and you are starting to get into inlay, which is an art. Inlay is usually done on unslotted, unfretted and unradiused fingerboards first and then they are slotted, radiused, fretted and fitted to the neck.
Anything with angles like rectangles, triangles or stars are more difficult to do because of the bits being round (makes cutting a corner difficult. Filler is usually an epoxy (black for an ebony board).
Depending on material, cutting shapes can be difficult. You can get a couple of common ones from
Stewmac and others, but anything else and you have to make your own. Cutting shells like pearl and abalone requires a decent set of specialised tools.
