My advice would be to declare any and all mods. Just to be on the safe side more than anything.
Despite what people might tell you...you have no garuantee that the insurers won't check your car after a smash. Remember that insurance companies will do ANYTHING to get out of paying out...so if they can find the slightest reason to null your cover they will.
Personally I'd rather pay £400 extra for the insurance rather than take the risk of having to pay the consequences.
Sorry if that sounds a bit dramatised...but I find it is always better to err on the side of caution.