I tried %g/%d_cdrm/%d_cart but that didn't work.
it depends on what you want the save/snap name to be
if you run "mess pce -cart cdsys -cdrm draculax", your try would give you a save state names
(system + the cdrom name + cart name, because it's what you asked for with that option)
if you want it to be in a folder named only pce/draculax you just use "%g/%d_cdrm"
but then you will need to change it to "%g/%d_cart" when you go back to PCE cart games