Should people be allowed to modify their private property?

Should people be allowed to modify their private property?

...

As long as the car is still legal, why wouldn't they?

No.

As a europenis I believe the stock form must be preserved.

Assuming it doesn't endanger other people while being operated on public property and is registered to operate on said property, yes.

The laws in most countries (incl. the US and most US states) do not fully agree with me though.

as long as it is at least as safe as the original car to other road users

In my country you lose your license for things like installing better brakes or wider tires. Yep.

I believe it; I grew up in Germany where they are crazy about that shit.

Here in Alabama, USA though, anything fucking goes... Except drugs, gotta love that 10-year sentence for 1 weed plant. -_-

As far as I know, in most of the united States you can modify your car however you want. However, to use that car on publicly owned roads you must conform to public laws and regulations.