The definition of a modification varies from insurer to insurer. But generally speaking, it’s any change that differs from the manufacturer’s original factory specification.
Car insurance and disability modifications
As with any vehicle modifications, it’s important to tell your insurer about them in advance to make sure you’re properly covered.
Some mods can decrease your premium, if they make yor car safer some can make it increase especilly if they increase the value of the car, or make it more desirable to steal or more to fix and or replace.
In your case i cannot see it costing more for the mods more i would say if you had a hoist fitted.
Might be best to actually call the companies you get quotes from and speak to them as my insurance worked out cheap on the phone as i could get my private reg to register so had to call them and others i caled to see if they took the claim history letter as no claims discount or not and all i called did.