Question1: 

Purchase return -Assessee is engaged in manufacturing of Bidi, he purchase Jardi-Raw Tobbaco in May 2017, which was exempted from tax in earlier law, but in GST regime it is taxable, now he intend to return the said goods to supplier due to quality issues. In this case GST applicable, it is to be treated as supply under Section 142(1) of CGST Act, 2017? Or He can send / return such goods without GST?

Answer:

Your observation is correct it is to be treated as fresh supply and will be taxed 

Section 142: Miscellaneous transitional provisions      (Relevant Rule 118, Rule 120)

(1) Where any goods on which duty, if any, had been paid under the existing law at the time of removal thereof, not being earlier than six months prior to the appointed day, are returned to any place of business on or after the appointed day, the registered person shall be eligible for refund of the duty paid under the existing law where such goods are returned by a person, other than a registered person, to the said place of business within a period of six months from the appointed day and such goods are identifiable to the satisfaction of the proper officer: Provided that if the said goods are returned by a registered person, the return of such goods shall be deemed to be a supply. (Reply dt. 26/09/2017)