The Central Board of Excise and Customs constituted under the Central Boards of Revenue Act, 1963 (54 of 1963), may, if it considers it necessary or expedient so to do for the purpose of uniformity in the classification of excisable goods or with respect to levy of duties of excise on [such goods or for the implementation of any other provision of this Act], issue such orders ,instructions and directions to the Central Excise Officers as it may deem fit, and such officers and all other persons employed in the execution of this Act shall observe and follow such orders, instructions and directions of the said Board :

Provided that no such orders, instructions or directions shall be issued -

(a) so as to require any Central Excise Officer to make a particular assessment or to dispose of a particular case in a particularmanner; or

(b) so as to interfere with the discretion of the Commissioner of Central Excise (Appeals) in the exercise of his appellate functions.