best to mention it to them, as the car is not factory.
A new and young driver doing anything out of the normal ordinarily gives the insurer excuses to increase premiums & or to immediately revoke your existing insurance as modifications breaches your existing contract.
Maybe cheaper to simply modify it back to original & keep within your existing insurance contract terms & conditions if minimal overall costs are a priority?
Probably best be on the safe side. Pretty sure you're good if you're upgrading parts that are OEM and were available on your car, for example fitting alloys from a same generation model. Otherwise half the people driving used cars would be uninsured. It's a bit of a grey area though. OEM alloys have to be declared? What about aero wiper blades? You got the original dealership options receipt for those alloys? You get the point.
I'm sure you could plead ignorance if they ever bought it up but not the smartest move.