Limousine Safety Modernization Act This bill modifies the definition of "manufacturer" in motor vehicle safety provisions of federal transportation law to include a person who alters a motor vehicle that has already been purchased by the first purchaser by increasing the wheelbase of the vehicle so that it has increased seating capacity (e.g., a limousine manufacturer). A "first purchaser" means the first purchaser of a motor vehicle or motor vehicle equipment other than for resale.