Can the libero replace a middle blocker who has rotated to the back row?

The libero can replace a middle blocker who has rotated to the back row, which is why this answer is correct. The libero is a specialized defensive player designed to enhance a team's ability to receive serves and dig attacks, and they can substitute in without affecting the team's regular substitution count.

When the middle blocker rotates to the back row, this opens up the opportunity for the libero to step in, offering tactical advantages by allowing the team to maintain their strongest offensive players at the net while still having an effective defender in the back row. This flexibility is a key aspect of the libero's role and contributes to strategic gameplay in volleyball.

In contrast, the other answers imply limitations that do not align with the rules governing libero substitutions. The libero has distinct rules that grant them unique strategic advantages, making this substitution possible regardless of the player's condition or frequency of substitutions within the match.