buy asking for it after the clame would save them the money of a pay out
If they issue you a certificate of insurance after you have you declared all mods and they then refuse to payout you will have a case against them.
Providing you can prove all mods have been declared correctly then you should be in the clear. To be really *rec of the tum* about all of this you could take photographs of all of the mods to back up your declaration.
If this is stringently adhered to by all agencies then this is going to have serious repercussions in the aftermarket parts industry plus there are going to be a lot of cars where people who think they are covered and have no idea of this legislation will be driving illegally. No doubt the insurance companies will say ignorance is no excuse even though they issued the certificates.
What a right load of bovine excrement.