I'm not sure just the panel filter would have to be declared as it is a direct replacement and officially does not give any advantages apart from its ability to be reused. Possibly an induction kit or more would have to be declared. Plus, what if you bought a standard used A500 & it already had a BMC filter in, how are you supposed to know? :-)

Now there's no need to be a pedant..

There was a bit of case law a few years back, a guy had an accident in his BMW.  He had non-runflat tyres fitted.
His insurance company refused to pay out as the car was originally meant to have runflat tyres fitted.
It went to court, he argued like God knows what but still lost.

The moral of the story?  If you are 100% honest and upfront with everything, you've got no cause to worry.

My insurance went up by £5 when I told them about my optional-extra Skydome.  Their justification is, and rightly so, the car is A; worth more, B; technically more of a risk for damage, C; if I were to have an accident they would need to replace it with another car of the same spec.

Granted point C is a mute point as you can't order them any longer, but you get the idea