Because, this is very interesting :)
You can use the elem.property function to change the properties of existing (or new) elements. In this case, we would use the property "Properties" which is used for special/unique properties (e.g. conductivity, neutron penetrating etc). For changing WOOD, the line would probably be elem.property(elem.DEFAULT_PT_WOOD, "Properties", elem.TYPE_SOLID + elem.PROP_NEUTPENETRATE + elem.PROP_CONDUCTS + elem.PROP_LIFE_DEC). However, if you want to conduct more than once, you will also need to use elem.property(elem.DEFAULT_PT_WOOD, "Flammable", 0), since SPRK ignites flammable materials (except for INSL). This also has the (potentially undesirable) side effect of making WOOD immune to fire. SHLD has a very similar process, but without elem.PROP_NEUTPENETRATE (which is a default property of WOOD but not of SHLD), and without changing the "Flammable" property since SHLD is already immune to fire.