Hello Thomas,
If I'm correct in understanding that you're asking whether it's possible to specify a different graphic for every single key on across the full compass of the keyboard (or every single key in an octave), then indeed that can't be done in the CODM.
The CustomDisplayKeyboardStyle table is used to specify the images for the various key shapes possible (C/F, D, E/B, G, A, sharp, etc.), and those images would then apply to all octaves.