currently autostart.sh (and the backing menus) has code like:
if [ "$emu" == "edit_custom_res" ]; then
As such, an image file can be placed into rpi2jamma/snaps/edit_custom_res.png which will be shown when that menu item is selected.
Would be nice to have a prefix, e.g. "_edit_custom_res.png" so that there's no conflict between the menu item image in snaps and any rom snap that might be there.
Better still (although I dont think lemonlauncher supports it) would be to pick up menu snaps from a different folder, e.g. rpi2jamma/menusnaps