Section 254. Optional tax on prior mortgages

Whenever any mortgage other
  than a mortgage specified in section two hundred and sixty-four has been
  recorded prior to July first, nineteen hundred and six, the record owner
  thereof may file with the recording officer of the county in  which  the
  real property, or any part thereof, on which said mortgage is a lien, is
  situated, a written statement under oath verified by the record owner or
  the  agent  or  officer of such record owner describing such mortgage by
  giving the date of the same and the liber and page of the record thereof
  together with the names of the parties thereto,  specifying  the  amount
  then  remaining  unpaid  on  the debt or obligation secured thereby, and
  electing that it shall become subject to the tax prescribed  by  section
  two  hundred  and  fifty-three  of this chapter. Whenever any unrecorded
  mortgage has been executed and delivered prior to July  first,  nineteen
  hundred  and six, the owner thereof may record the same upon filing with
  the recording officer a similar statement and paying the tax  as  herein
  prescribed. A tax shall thereupon be computed, levied and collected upon
  the amount of the principal debt or obligation unpaid at the time of the
  filing  of  such  statement,  or  of  the recording of such mortgage and
  filing of such statement. On the payment of such tax as herein provided,
  the recording officer shall note on the margin of  the  record  of  such
  mortgage  the  fact of such statement and of the amount of the tax paid,
  attested by his signature, whereupon  such  mortgage  and  the  debt  or
  obligation  secured  thereby  shall  be  entitled  to the exemptions and
  immunities conferred by this article, and all of the provisions of  this
  article  shall  thereafter  be applicable to said mortgage. Whenever the
  original mortgage is presented to the clerk together with the  statement
  he  shall  also note on said original mortgage the fact of the filing of
  the said statement and also the amount of the tax paid duly attested  by
  his  signature,  which  indorsement  shall be conclusive evidence of the
  payment of such tax.