Section 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.