And how do you propose to do *that*?
In Europe, anything you do to your vehicle has to be accompanied by "the certificate". Every part that serves any function which is even remotely related to the vehicle's compliance with any mandatory standard. Want to change the exhaust system? The new one had better be "e-marked", and that means both noise and emissions - no catalyst removal allowed, if it came with one, it has to be there and it has to work. Want to change the turn signals? No crappy dim LEDs allowed. No "integrated" turn signals with insufficient brightness, insufficient separation between left and right signals, etc. It all has to have the applicable "e-marking" and/or the applicable documentation from the manufacturer stating that it conforms to applicable standards. And you have to bring the vehicle in for inspection every year or two to the MoT (UK) or TuV (Germany) and they check all that stuff. No forging e-markings, either - they'll ask for the documentation. Don't have it? you fail. Faked documentation? Doesn't work - you fail. "Made in China" parts with declarations of conformity worth exactly what the piece of paper that they are printed on is worth? FAIL and they'll go after anyone selling that stuff in the market. Put all your "good" parts on to pass TuV then take it off right after? The "polizei" know the difference, they'll pull you over and do a roadside inspection. Fail.
This does have the effect of keeping a lot of aftermarket garbage off the market, but it is a hassle, and it certainly limits one's freedom of expression when it comes to customizing your bike. There is a presumption that the vehicle's original manufacturer knows best - you're not even allowed to use tire sizes different from what the manufacturer prescribes. All of the motorcycles that I saw on the road in Germany were completely stock.
I don't think you want to go down that road. I sure don't.