You'll have a choice, but the fact that you are retired limits your options considerably. That's because MRA + 10 retirements are unique to FERS. You may not be eligible to retire under CSRS, where you need 30 years of service to retire at 55. As a retiree, your choice would be to stay in FERS with an MRA + 10 retirement, or choose CSRS Offset and wait until age 62 to receive a deferred retirement.
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