If you’ve bought your new car from an authorised dealer and opted for extra features, such as alloy wheels, it shouldn’t affect your premium too much as they’ll have been fitted according to the manufacturer’s specifications.
However, if the modifications increase the value of your car, you may pay a slightly higher premium than you would for the basic model.
If you're buying a second-hand vehicle that’s been modified, make sure you get all the details of the modification and pass them to your insurance provider.