IMO you should fight those fines, you are allowed to modify your vehicle acording to transport legislation. As I outlined before you can do "simple mods" without an approval so long as they comply with certain legislation (ie noise and pollution req's) If a cop fines you, take it to court, it's simple and it's the only way.
Scarface: That cop is probably referring to the "hoon legislation" which has been in effect for ages. Chances are he is, like many police, without any idea of the law and wish simply to frighten modified car owners with false information.