Section 12. After section 151 of the principal Act, the following section shall be inserted, namely:

12. After section 151 of the principal Act, the following section shall be inserted, namely: "151A. The Board may, if it considers it necessary or expedient so to do for the purpose of uniformity in the classification of goods or with respect to the levy of duty thereon, issue such orders, instructions and directions to officers of customs as it may deem fit and such officers of customs and all other persons employed in the execution of this Act shall observe and follow such orders, instructions and directions of the Board: Provided that no such orders, instructions or directions shall be issued— (a) so as to require any such officer of customs to make a particular assessment or to dispose of a particular case in a particular manner; or (b) so as to interfere with the discretion of the Collector of Customs (Appeals) in the exercise of his appellate functions."