§ 400-a. Exceptions to registration provisions. Notwithstanding any inconsistent provision of this chapter or other law or regulation, the commissioner may refuse to register any vehicle or class of vehicles for use on the public highways where he determines that the characteristics of such vehicle or class of vehicles make such vehicle or vehicles unsafe for highway operation. Provided, however, that such authority shall not extend to any vehicle which is eligible for registration as a special purpose commercial vehicle under the provisions of schedule F of subdivision seven of section four hundred one of this chapter.