As a broker we would compare rates and coverages with different insurance companies. Each one of those companies has their own rules or "appetite" when it comes to mods and upgrades. Our job is to find the right fit for you and your bike.
Personally as a rider I know that if installed professionally, upgrading the shocks could make the bike handle better. In this particular case it is a mod that doest not need to be noted on the policy or for a quote as it does not alter the performance (hp, torque, throttle control, rake, trail, etc) of the motorcycle. That being said mods and upgrades that do change the performance or geometry of the bike do need to be disclosed by the client so both the client and insurance company are clear on the bike that is being insured.