I am insured with Quinn mate. I've got quite a few modifications but as long as your modifications dont affect the cars performance then Quinn dont care and it wont affect your premium at all, you dont even have to tell them. It even says it on their homepage if you would like to check.
I'm also insured with Quinn and even some performance mods dont affect your premium. Only thing I've found that they increase it for is a larger engine but as clutch said its best to make sure. :thumbs_up: