Modifying cars and insuring them is always going to end in tears for some people. I have known some to buy a modified car and then find they cannot insure it. What happens next? They decline to inform the insurance company of the mods done, a ticking timebomb!
There is no middle ground on this, do your homework and shop around before you entertain any modifications. Also get clarity on what is and what is not covered. Some companies will insure modified cars but in the event of a claim you will not get like for like replacement parts or in the event of a write off, you will only get the current market value for a standard version.
I have modified insurance with every modification declared, including the remap and I have full like for like cover which includes total coverage if it is written off.
Terminology, nice if it worked but when reading a stainless steel long life exhaust or servicable conical element air filter will still be categorised as aftermarket exhaust and induction kit!
On my form they also asked who carried out the work and what their qualifications were. In my case I said I did the work and was a time served toolmaker with nearly 30 years engineering experience and with a Masters degree in engineering, think that might have helped?