Similar to this, I always wanted to be able to turn a replacement for the Samsung "S-pen" on my Galaxy Tab S6, but aside from the replaceable tip (just a simple chunk of plastic) there's just too much circuitry involved - the bit that holds the pressure-sensitive tip, the antenna, the battery and charging circuit, plus a few assorted magnets - and too much of it seemed to be dependent on the molded shape of the exterior to hold it all in place. There were no convenient "guts" that could be extracted and re-mounted. Replacements were also awfully expensive to experiment on.