I splitted the thread. When starting a new subject, please make a different thread, otherwise it gets too messy. 
  Now, I am not sure of what you want to do. Do you want to remove a disguise effect, simply unequip a npc or also remove the item from inventory? 
 Here is a script to simply unequip a NPC. 
 void main ()
 { 
 object oNPC = GetObjectByTag("my_npc");
 object oArmor = GetItemInSlot(INVENTORY_SLOT_BODY,oNPC); 
 AssignCommand(oNPC, ActionUnequipItem(oArmor, TRUE));
 }  
 Other body slots: 
 int INVENTORY_SLOT_HEAD = 0;
 int INVENTORY_SLOT_BODY = 1;
 int INVENTORY_SLOT_HANDS = 3;
 int INVENTORY_SLOT_RIGHTWEAPON = 4;
 int INVENTORY_SLOT_LEFTWEAPON = 5;
 int INVENTORY_SLOT_LEFTARM = 7;
 int INVENTORY_SLOT_RIGHTARM = 8;
 int INVENTORY_SLOT_IMPLANT = 9;
 int INVENTORY_SLOT_BELT = 10;
 int INVENTORY_SLOT_CWEAPON_L = 14;
 int INVENTORY_SLOT_CWEAPON_R = 15;
 int INVENTORY_SLOT_CWEAPON_B = 16;
 int INVENTORY_SLOT_CARMOUR = 17;  
 To remove a disguise effect, you woulf use the followin: 
 RemoveEffect(object oCreature, effect eEffect);  
 and finally to remove from inventory, check the script I posted in this thread: 
http://www.lucasforums.com/showthread.php?s=&threadid=129600) (thread is about regeneration but the script can be used for any item)