Do these vents require any drilling or modification to the fender?

No. These scoops are engineered to use factory fender bolt points. Simply align the mounting holes and secure with the appropriate fasteners. Verify your vehicle's fender hole locations before installation to ensure clean fitment.

What prep work should I do before paint?

Sand the surface with appropriate grit to scuff the finish, then clean away all dust. This creates proper adhesion for your chosen paint system. Follow your paint manufacturer's instructions for primer and topcoat application over FRP.

Will these vents actually increase air flow, or are they cosmetic?

These are styling vents designed for the N Spec look. They do not function as functional air intakes. If you need genuine cooling or engine bay ventilation, confirm your engine bay setup independently to avoid disappointment.