| Todd, if you plan to use the original cavity you will probably need the inlays as a pattern to cut the replacements from. The inlay itself is much easier to use for a pattern than the cavity thats left when you remove the inlay.
You can remove most inlays with the careful application of heat if they are not made from pearloid, a plastic material (celluloid) that can be pretty sensitive to heat.
If they are abalone or most any other non-manmade material, the heat is not likely to hurt them unless you put way too much heat on them.
You can simply heat the tip of a pin or needle and very lightly touch the hot point to the inlay. If it marks (melts) the inlay, heat will still remove it but chances are high that the inlay will deform enough to make it useless as a pattern for the new inlay.
Normally, the inlays are cut first and then the cavity is cut to fit the inlay. It is much harder to cut the cavity (or use an existing cavity) and then try to cut an inlay that fits properly.
Another point is that, normally, sanding dust from the fingerboard material is mixed with glue to make a matching filler. Since the cavities already are there, you will need to find a scrap of wood that matches the fingerboard to make the filler from. Any color mismatch will stand out like a sore thumb. Even the experts have to resort to fillers for hand cut inlays.
What material do you plan to use for the inlays, and what is your fingerboard material?
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