interesting......im quite sure this law doesnt exist, I rang RTA the other day and they are under the opinion that there isn't any law against changing your bonnet or its shape as people have been doing it for as long as cars have been around. Crumple zones havent got anything to do with it, the bonnet isnt counted as its classed as a "weak" feature of the car from the start. Whether its a standard or aftermarket option it will still crumple easily as it has no real support and has no real place in reducing the impact to a car. I suppose you only have to look at GTR's that have aluminium bonnets, they would hold up about the same. Despite this i have no doubt police would try to book you for it, however no law = contensting....