Can the Advance Ruling pronounced under Section 98 or 101 be rectified

Yes. The Authority or the Appellate Authority may amend any order passed by it under section 98 or section 101, so as to rectify any error apparent on the face of the record, if such error is noticed by
 the Authority or
 the Appellate Authority on its own accord, or
 is brought to its notice by the concerned officer,
 the jurisdictional officer,
 the applicant or
 the appellant
within a period of six months from the date of the order:
However, no rectification which has the effect of enhancing the tax liability or reducing the amount of admissible input tax credit shall be made unless the applicant or the appellant has been given an opportunity of being heard.

(ICAI FAQ PUBLCATIONS Advance ruling under GST: FAQ NO. 20)

What are the powers of Advance Ruling Authority and the Appellate Authority for Advance Ruling

The Advance Ruling Authority and the Appellate Authority for Advance Ruling shall have all the powers of the Civil Court regarding;
(a) discovery and inspection;
(b) enforcing the attendance of any person and examining him on oath;
(c) issuing commissions and compelling production of books of accounts and other records. Further, the Authority or the Appellate Authority shall be deemed to be a civil court for the purposes of section 195, but not for the purposes of Chapter XXVI of the Code of Criminal Procedure, 1973, and every proceeding before the Authority or the Appellate Authority shall be deemed to be a judicial proceedings within the meaning of sections 193 and 228, and for the purpose of section 196 of the Indian Penal Code. Further, if the Advance Ruling Authority and the Appellate Authority for Advance Ruling finds that advance ruling has been obtained by the applicant or appellant by fraud or suppression of material facts or misrepresentation of facts, it can declare such ruling or Order to be Void ab-initio.

(ICAI FAQ PUBLICATIONS Advance ruling under GST: FAQ NO. 19)

Where will the Appellate Authority for Advance Ruling be located

The Appellate Authority for Advance Ruling constituted under the provisions of a State Goods and Services Tax Act or a Union Territory Goods and Services Tax Act shall be deemed to be the Appellate Authority in respect of that State or Union territory. However, the Government may, on the recommendation of the Council, notify any Appellate Authority located in another State / Union territory to act as the Appellate Authority for the State or the Union territory where Appellate Authority for Advance Ruling is not constituted.

(ICAI FAQ PUBLICATIONS 06-09-2017 Advance ruling under GST: FAQ NO. 13)