Either or. Tuning on the Jap cars always means external addons, which I think looks perfect on the Impreza, but that’s the only Jap car I like anyway.
But tuning the high-class stuff like Lambo and Merz and Bugatti is always internal. Tweaking the engine, upping performance, and putting on a new pair of hubs. It looks basically the same as what rolled out of the factory, but the refined engine makes it unique. So it depends on the car.