When it comes to insurance, you're better off telling them and for them to say 'we don't need to know about that' than not telling them and it voiding your insurance come payout time, if it's not standard, tell them.
Looking at your profile picture it looks like you've got a Mk2 Active so probably a 1.2 8v? This is just my opinion but you'll soon want something faster (as I'm guessing you've not long passed your test?), so I wouldn't waste my money modifying a car that can be resold easier on the basis of being a base model, you start adding mods and it's going to be harder to sell as buyers will think you've been ragging it. Keep it clean and tidy and in a couple of years, upgrade to a Sporting or an HGT and work with that instead.
As I say though, that's just my opinion