In a word, yes.
All modifications in theory should be declared. Depending on what they are/ who the insurer is, they may want some more money out of you.
In the even of a claim, if you have undeclared mods, they could refuse to cover you.
Agree 100% with this.
@Baily.l; pretty much all insurance companies will include a requirement in the small print of their policies for customers to declare
any modifications. This gives them the opportunity to assess any increased risks that they consider a modified car represents compared to an equivalent unmodified car, and whether or not they need to charge any extra premium.
Realistically, insurance companies are probably more concerned with performance related mods than they are with cosmetic mods. However, certain cosmetic mods can make a car more attractive to would-be thieves. It might also cost more to repair a car with cosmetic mods if it was involved in an accident - e.g. additional time and expense spent sourcing the parts and fitting / painting them when repairing the car compared to a non-modified car.
I have a set of aftermarket alloys on my current car (I also had non-factory alloys fitted to my previous two cars). On the first car and my current car, my insurance company didn’t require any additional premium. On the second car, they charged me something like an additional £15 - £18 per year (can’t remember the exact amount).