Not sure if this is the right thread for this but it was the best I could find;
Watching an advert for Hyundai on Sky One I noticed that at the end it listed the local Hyundai dealerships in the same way that the old ITV regions used to do. I highly doubt it was national as it listed only two dealerships, both in Yorkshire which makes me wonder how they managed to do this given how, as far as I know, the channel isn't split into advertising region like Channel 4 or Channel 5 is or was.
Thats called AdSmart. It basically checks your location, or changes an advert.
To take it further, the advert is stored on your Sky+ box and synced up to play in the place of another advert.
Sky also have PromoSmart which can do the same for Promo's, even down to Street level.
If you want to opt out there is an option on the Sky website.