In v6.08 of ROOT, you could modify the mean/median marker of violin plots with
hviolin->SetMarkerStyle(20);
hviolin->SetMarkerSize(0.5);
as here: ROOT: THistPainter Class Reference (cern.ch). However, it seems in v6.20 these options no longer affect the mean/median markers, as seen here: ROOT: THistPainter Class Reference (cern.ch)? Is there a way to modify their appearance still?