I havent seen the official rules for SoF. But, the core rules say if a dice roll uses multiple dice you must reroll all dice with the command reroll strat. Unless the SoF rule says otherwise.
RE-ROLLS
Some rules allow you to re-roll a dice roll, which means you get to roll some or all of the dice again. If a rule allows you to re-roll a dice roll that was made by adding several dice together (2D6, 3D6 etc.) then, unless otherwise stated, you must re-roll all of those dice again.