It can be quite hard, however if you are using an experienced body shop you should be fine.
I've heard of a few isolated dramas, however remember that most people have a spark plug cover. It may cause a drama if you have a vented coil pack cover and you leave it in the rain.
Nobody that I know sells ADR approved bonnets. Having said that, I have also never heard anybody first hand have dramas with the police. I have heard stories from peoples brothers half sisters long lost cousins husbands kid had a run in with the police, but I don't really trust them.
I can confirm that we don't sell them for series 2, as for others I'm not sure. FYI we have the blazer style for the series 2.