Last car i had, had a K&N Filter and a cat back ss exhaust.
I insured it with elephant, declared the mods later and they charged me and extra ?11. ?6 of that was admin for doing it on the phone! I also removed my imobiliser after it went wrong, i told them it now didn't have one and they charged me just the ?6 admin fee for changing the policy details.
So in my experience elephant are good for mods.