Forgetting to declare mods is Fraud, will make your insurance void, and you're going to be more F**ked if you later make a claim and they find out. Sure you might remove your air filter, but can you strip out a T34, coil overs, stainless exhaust etc etc after you've rolled your car and before the assessor sees it?

No.

I had to wait till I was 24 with 7 years no claims before my Cossie insurance became affordable (£1k or less), but it was worth the wait and i drive round knowing the car is road legal, and correctly insured.

If you have done a lot of mods which you can't insure you may have to bite the bullet and go back a stage or 2, but at least you'll be legal, which while boring is deffo the best way to drive.

Simon