Is it a mod that you’ve declared to insurance?
It's no different to slapping a big GB sticker on the back.
Yes, it is a big sticker, but I suppose an insurer might consider there are additional costs of getting the roof re-wrapped if the roof became damaged and needed to be repaired, in which case it’d cost the insurer more to settle the claim to return the car to its pre-damaged state.
You could also say a car that’s been completely vinyl wrapped doesn’t need to be declared as it has just had a large sticker applied; I think pretty much all insurers would expect an owner to declare if they’d had their car wrapped.
I’d declare it - better to be safe than sorry and avoid the potential issues of an insurer being difficult over paying any subsequent claim if the OP is unfortunate enough to need to claim in future.