it is perfectly legal to reshell a car using a new shell and keep the original identityinsurance companys do this on very young vehicles.....you are only replacing a part of the car.
i have sold hundreds of fords over the years and had things like rs turbo,s at under a year old that have been reshelled BY THE INSURANCE COMPANY and have not been write offs and have kept original plates and are perfectly legal

it is only illegal if you reshell an existing car with a secondhand shell and try to change the id