The brief answer to this question is: It is generally not possible to "reopen" or modify the division of property after a Georgia divorce has been finalized. However, like many legal concepts, especially laws concerning divorce and family law, there are some exceptions to this general rule.
In Georgia, a determination made by a judge or jury concerning the equitable division of marital property, such as a retirement account is not modifiable. According to Georgia law, if the final judgment and decree of divorce in a case purports to settle all issues regarding property division, revision or modification of the provisions of the divorce decree regarding the equitable division of property is not permissible. Holler v. Holler, 257 Ga. 27 (1987). Thus, if a divorce is finalized and one spouse's retirement account was not divided in the divorce, one party may not subsequently reopen or modify the Final Divorce Decree to obtain a portion of that spouse's retirement account.
However, one exception to this widely held rule concerning the modification of property settlements in Georgia is that a final divorce judgment may be set aside if "The judgment was obtained as the result of fraud, accident, or mistake or the acts of the adverse party unmixed with the negligence or fault of the movant […]. See O.C.G.A. §9-11-60. Thus, if one party deliberately deceived the other party regarding a significant matter, such as the existence of a retirement account or the exact value of the retirement account, and the divorce judgment was based on this deceit, the other party may be entitled to have the divorce judgment set aside. If the party seeking to have the divorce judgment set aside is successful, the entire divorce judgment will be set aside. Additionally, if the person seeking the judgment to be set aside has received benefits for the judgment, such as property or asset awards, these benefits must be returned while the matter is being re-adjudicated. O.C.G.A.§§ 9-11-60(f) and 9-11-60(d)(2).