Benefits are limited as follows:
1. One benefit only. A beneficiary may select only one benefit, regardless of how many benefits the beneficiary qualifies for; and
2. Election final. Except as provided in section 18403, subsection 4, and section 18553, subsection 8, if a beneficiary elects a benefit after receiving reasonable notification of available options from the retirement system, the beneficiary's election of a benefit is final and may not be changed or revoked at a later date.