We have the same system for singleplayer troops as well, generally we have a pool of 3 equipment sets for each troop, which get chosen randomly by each troop.
The way the changes go are related to the tier troop. For low tier troops, the torso, shoulder, head, gloves all tend to change to give them a less uniform look. Mid to high tier troops generally wear the same torso but change shoulder and head armors. The highest tier troops all wear the same uniform.