O.C.G.A. § 48-13-113 (2019)

(b)(1) If a municipality located within a special district where the excise tax is imposed by the county is not participating in such excise tax and is not receiving proceeds of that excise tax, the governing authority of that nonparticipating municipality may give written notice to the governing authority of the county and the governing authority of each participating municipality within the special district of its decision to opt in to the existing intergovernmental agreement. Within 60 days of the date of such notice, an amended intergovernmental agreement shall be executed by the governing authority of the municipality exercising such opt in and the governing authorities of the county and each currently participating municipality.

(2) When an amended intergovernmental agreement is executed pursuant to paragraph (1) of this subsection, the revised distribution of proceeds thereunder shall not become effective until the first day of the next succeeding calendar quarter which begins more than 80 days after the execution date of such amended intergovernmental agreement. The distribution of proceeds of the excise tax shall continue under the prior intergovernmental agreement until the date provided for in this paragraph.