It is not legal in the US, period.
10751. (a) No person shall knowingly buy, sell, offer for sale, receive, or have in his or her possession, any vehicle, or component part thereof, from which any serial or identification number, including, but not limited to, any number used for registration purposes, that is affixed by the manufacturer to the vehicle or component part, in whatever manner deemed proper by the manufacturer, has been removed, defaced, altered, or destroyed, unless the vehicle or component part has attached thereto an identification number assigned or approved by the department in lieu of the manufacturer's number.
http://forums.officer.com/t130658/