i wouldnt think so.. as long as the alloy design is the same, it wouldn't be any different from the stock alloys.
I know a great shop in Swindon, Wiltshire that is owned and run by auto enthusiests. I can get you thier information if you want.
i told my old insurence company when i added painted alloys and stripes onto my mums old swift and the price didnt go up, so i dont think they are clased as modifications!
Cheers, only problem is i live between aberdeen and inverness lol I think there's a place in Elgin im gonna try. Dont know if anybody knows of any other places this far north?