Manufacturers have been shipping cars with detuned engines forever, and tuners have been tweaking them to unlock the hidden power for just as long. Back in the beginning of the century I owned a 2000 Audi S4 twin-turbo. The torque curve on it looked like a perfect plateau between 2,500 and 5,300 rpm. I replaced the entire ECU with a chipped duplicate (a five minute swap) and instantly gained 50 horsepower. Of course, Audi limited the torque for a variety of reasons, including reliability and the fact that otherwise the car would have encroached on their higher-end RS4 line.

Similarly, the car I have as a track toy, a 1986 Porsche 944 Turbo, was famously limited by Porsche to avoid competing with their flagship 911 Turbo. Tuners figured this out and came up with all sorts of modifications, from mild to wild, to extract more performance.

Back in the 2000s I didn't have a problem with insurance. Probably not the same today.