The entry you located is for the same man described in my post, John J. Cumbie of Campbell County VA, Co. "I", 42nd Virginia Regiment. He was about age 26 when enlisted in 1862.

A soldier cannot be a civil servant, just as a civil servant cannot be a soldier. Men in the army who received a civil appointment were released from service in the army; a civil officer who wanted to join the army would have to leave office to do so. "No man can serve two masters."

Based on what we've found so far, I would discourage use of the term "runner" to describe what this man did in the army.