[coolfile]

Here is some code. the problem is that the weaponset cann't be changed back. It becomes one way upgrade indeed.

  WeaponSet
    Conditions = None 
    Weapon = PRIMARY ChinaInfantryTankHunterMissileLauncher
  End
  WeaponSet
    Conditions = PLAYER_UPGRADE
    Weapon = PRIMARY ChinaInfantryNapalmHunterMissileLauncher
  End

  CommandSet      = ChinaInfantryNapalmHunterCommandSet

  Behavior = WeaponSetUpgrade ModuleTag_13
    TriggeredBy = Upgrade_ChinaNapalmHunterWeaponSet
  End

  Behavior = CommandSetUpgrade ModuleTag_14
    TriggeredBy = Upgrade_ChinaNapalmHunterWeaponSet
    RemovesUpgrades = Upgrade_ChinaTankHunterWeaponSet
    CommandSet = ChinaInfantryNapalmHunterCommandSet
  End
 
  Behavior = CommandSetUpgrade ModuleTag_15
    TriggeredBy = Upgrade_ChinaTankHunterWeaponSet
    RemovesUpgrades = Upgrade_ChinaNapalmHunterWeaponSet Upgrade_ChinaTankHunterWeaponSet
    CommandSet = ChinaInfantryNapalmHunterCommandSet
  End
 
  Behavior = ProductionUpdate ModuleTag_16
    MaxQueueEntries = 1; For the command set switching upgrade
  End

BTW, the WorldBuilder cann't detect the mistake when Hunterr is typed.