Take a look at my module guide if you want more information (points at signature).
But anyway, the ArmorUpgrade module (no it's not ArmorSetUpgrade) triggers a condition for the ArmorSet, called PLAYER_UPGRADE. This means that if a particular ArmorSet's conditions (None, PLAYER_UPGRADE etc.) matches the current conditions, the ArmorSet switches to that set. Anytime a condition occurs that is not in any ArmorSet, the "Condition = None" set is used. So you could easily put in an upgrade module for a WeaponSet or ArmorSet, but as long as there is no specific set connected to the PLAYER_UPGRADE condition, it will stay in its default state. Got that?
