If you have a static property, you can do elem.property(tpt.el.dust.id, "DefaultProperties", {["tmp"]=5}) This defaults the tmp to 5. Set other properties as needed.
If you need dynamic properties, use the Create function: elem.property(tpt.el.dust.id, "Create", function(i) tpt.parts[i].tmp = math.random(1,10) end)