Is it true that in Europe it's very difficult to modify your car like swapping engines or adding a spoiler to it without paying additional taxes or getting an approval by a mechanic?
Yes. This is also true of California, my uninformed young friend.
>>78159441
yes, it's true here
most modifications are illegal and the police will arrest your car afterwards
Nope.
Ofc if you don't tell the insurance company about them then you're technically uninsured. Switching the engine block itself you would need to tell the DVLA (on paper) as it'll change displacement