Maybe there a way to write a custom format in Edit->Preferences->Display->Name Format to display part of a Surname in the chart (Eg: Schwarzendruber as sh). I am not aware of how to do it.
My idea is a to print a chart with all members of a certain family along with 2nd cousins and their family names. Since there is not much real estate in the chart, I wanted to show a short family name with a legend on the side of the chart. This monogram helped, even though it may not be the most elegant way.
[Gramps SuperTool script file]
Individus-Sort_as des individus groupés
for n in nameobjs:
n.sort_as = -1
([n.group_as, n.sort_as, n.display_as] for n in nameobjs)