Sorry - I know this doesnt directly answer your questions, but I thought I should mention.
Insurers see it as a handling modification (what I was told). So I would tell them - if you havent told them - you wont be covered.
Now regardless of whether it improves the handling or not, they will still no doubt want you to part with some extra cash for the pleasure - if they will insure you at all!!
My previous insurers were Hastings Direct - got a fantastic renewal quote, but as I was going to add spacers to mine, I thought that I had better mention it - they wouldnt insure me at all - as it was a "handling modification".
As I wanted to stick with the spacers, it took alot of looking to find an insurer who would cover me at all or without wanting another £300 in some cases - rediculous!