When you insure you will be asked the details regarding the car (generally you input the reg no. and it will find all these details automatically), then you will be asked about any modifications. It is vitally important to get these right, something as simple as the lights being changed can be the difference between a payout and no payout. The insurance companies are a business and are looking to make money, as such, following an accident etc they are looking for any excuse not to payout.
In my experience (as a young driver) having lexus lights and a bonnet scoop (fitted when I bought my car) added 30% to my premium and it was far cheaper to buy original parts from the scrappy than pay the extra.
Do your homework and check various comparison sites before insuring.