the only limits to what you can modify over here is the cost of insurance (assuming you can get covered in the first place)

my insurance has come down by £100 but it's only me to drive now and no one else
before i had any driver over 25 and my wife covered but now the company have said "too many mods" and refused
i can see it getting to the point where i won't be able to afford to run a modified car, but until that day, i'll keep modding