Can they do it? absolutely...unfortunately. Paddy has been fighting this for ages. As for flying a quieter aircraft his Spitfire has, from memory, a Lycoming? engine in it so it is very quiet any way...
Good luck Paddy...someone who is actually employing people through his engineering business, making things in Australia for use by Australians. Indeed a very rare person...probably why they're trying to shut him down, can't have someone actually doing something productive.