Just make 2 items. 1 equip and 1 unequip.
Make the items call a common event. (Not the same one)
Make the common event called by the equip item remove the equip item, add the unequip item and do whatever you want to happen when equipping the item
Make the common event called by the unequip item remove the unequip item, add the equip item and do whatever you want to happen when removing the item.