Insurance wouldn't give me full coverage on the Harley until i had it appraised, and they didn't spank me to hard on it.
for you i guess it is a question of, if you don't tell them and something happens, they are not touching what was done,
if you cover it and something happens, then it is covered
it is pretty scary approaching the insurance companies here about anything other then a stock bike, rates are insane here, certain areas here have the honor of being the highest rates in north america