Well, u can't add to abbilities cooldown just like writing it there. I think WE would be better with this feature, but back to the problem. Maybe i am not right, but i think u need trigger, or maybe i think a Jass script to do such a thing, and it may be pretty hard. Again, maybe i am not right. Or maybe just make an dummy ability, and make a unit is attacked, than remove Hardened skin from Triggering unit and add the dummy ( just not to look like it dissapeard ), wait 5 (or whatever u want) seconds, add Hardened skin to Triggering unit. Something like this