What a wonderful response! I will do my best to take your excellent advice. Also I will have more to say in future on this range of topics — next I will probably tackle .scl file format.

Chris Vaisvil removed the frets from a guitar, backfilled the the fret slots, and added cable ties as mobile, removable frets that he could position for just about any small octave divisor. He plays the resulting guitar in this video, which is his work, not mine. Text under the video includes how-to links and info.