Laws that allow for discretion are actually a good thing. On one hand, they let hackers be creative in areas where there isn't a specific prohibition, and on the other hand they let authorities squash things that were so obvious that nobody thought to pass a law against them.
It doesn't look like WD40 is being stomped by overbearing authority here- Dudley gave WD40 an off the record
"this car is all kinds of wrong" warning and a few weeks later wrote him the smallest ticket he could while still sending him to a garage for an inspection. Now that the garage has it, they're big fans of the aeromods but can't issue a roadworthiness sticker because of other issues. The other issues are the real problem here.
Random garages and insurance salesmen not being able to walk you through a rare situation isn't a surprise, and it's not the cop's fault here either. The system expects cars to get fixed at the garage, and it probably also expects people to be in for regularly scheduled inspections instead of being sent there by the police with registrations provisionally revoked.
Odds are, once the car gets a fresh inspection sticker it's good to go. At least on that car, it'd probably be best to integrate lighting to the mods in the future, just to avoid problems:
