They have agreed to cover it without self levelers and washers installed? Surely that makes it an illegal mod which won't be covered then? Just wondering as if I would declare it to mine if they let me
As a follow up to your question I would like to link you to this:-
so as of April 2012 they are legal as long as they are aligned properly (but that would only hinder and MOT test if they wernt, though you could risk a £30 fine is PC plod thinks they are not aligned). As for your levellers and washer jets query, they only need to be operational if your car has them fitted which the fiesta does not. So make sure their aligned then decalare away!!
Awesomeness!! Looks like mine are staying in!!