Not a material change
It is a minor cosmetic change to exterior trim that does not change the material colour or identification of the car, and it does not modify any of the mechanical/electrical/structural systems in any way so I do not think the insurance companies would care AT ALL. Its like tinting your windows or applying Supaguard paint protection. If this is an issue, you can always swap back to the standard grill at the end of your contract/lease. The Urban grills really add lift to the Mineral White car and i would strongly recommend you consider it.