As some people noticed, not all trait icons can be used in the scenario creator. However, if you edit the disease.txt file you can give the name of icons that can't be selected in SC. Using this trick you can use overlay icons as solid images and other icons as transparent overlays. With this method you can use icons used in genes selection, country specific (urban, rural, poor etc), the dead population skull icon, the dead ape population skull icon, the Christmas icons and many others.

The only problem is guessing their names. I would greatly appreciate if someone could find a way of seeing all the icon's names. Some of the unused icons look very useful.