§ 218. Special classification of vehicles. Notwithstanding any other provision of this chapter, any vehicle or class of vehicles may, by regulation of the commissioner, be added to or exempted from any of the definitions or classifications contained in this chapter, where such addition or exemption is deemed, in his discretion, either necessary, desirable or equitable because of the particular characteristics of such vehicle or class of vehicles; provided, however, that no vehicle which is exempted from registration by any provision of this chapter may be reclassified pursuant to this section to require registration, and no vehicle which is specifically enumerated in schedule F of subdivision seven of section four hundred one of this chapter may be reclassified pursuant to this section to require registration at an increased fee.