In a recent Ask June question, a veteran inquired if there was any way to go back and change the choices he made when he left the service. He was part of an overmanned field and was given a bonus to leave the service before reaching retirement eligibility. Unfortunately, the short answer is no - decisions made regarding separation packages are permanent.
Like decisions regarding separation packages, decisions made regarding the Survivor's Benefit Plan are rarely able to be changed. You need to be sure to carefully think through all the short-term and long-term implications of all the options before you make a final decision.
Even though you may not change the terms of your separation package, you may be able to make other moves that can work in your favor. A return to active duty or reserve status might allow you to reach retirement eligibility. Some federal jobs allow you to use your military service time towards your time-in-service pay grade and also towards a federal retirement pension.
When the time comes for you to leave military service, be sure to consider any benefits that might be offered to you and think about it from every angle before signing on the dotted line. Those decisions can't be undone!