Hey dude,
Im with wrxtatic on this one. Disclose every mod/change. I am with JCI and found them hundreds of dollars cheaper. (when vs RAC). ($1200 VS $2100). The offset for this is a higher excess/s to pay in an at fault claim. (Going on youngest driver - my partner). But really, if you disclose everything, you have the peace of mind of knowing things well get done right, and your car repaired to a level excepted by you. And the lower cost p/a I think outweighs the 'excess extra charges'. I mean, ideally, how many claims do you want to make a year, or ever? None.
So why pay so much more per year, to have low excess charges?
Just another food for thought,
Cheers,
Brent.