I just read that lilypond includes support for rightHandFinger events. Being a guitarist I was thrilled.
I ran the example and tried a couple of experiments to see if I could change the capital P and I that appear, in guitar the fingers are spelt in lowercase p, i, m, a.
\rightHandFinger #0 ... #11.
0 and greater than 5 appear as "x".
Is there a way to tweak the way it displays the fingerings?