This has previously been discussed here.
According to the Manual, I should be able to remove rows of frets. The editor does what I want, however the Save button remains greyed out after I have removed the surplus frets, so it is not clear to me what the purpose of the + and - fret buttons is, if the result of choosing them as per the manual is not saveable. I would like the reconfigured Chord Diagram to save locally to this instance.
Below screenshots show the unchanging greyed out status of Save:
DEFAULT:
DESIRED
The only way to make the number of frets displaying stick is via
Engraving Options → Chord Diagrams: Default number of frets, which applies to all chord diagrams in the entire score:
I would also like to be able to open the Chord Diagram for editing while in Write Mode, and am not clear why this is currently possible only in Engrave Mode.