I dont think thats really necessary since spirit already allows you to customize their behaviours in properties.
But I think you just want them to be hostile when you enter somewhere...
I never tried barneyinblue's way but you can make the soldiers friendly to gordon at first then put a trigger_once (targetting a trigger_relay) in that certain area and set that trigger_relay to kill all the friendly soldiers Also, put monster makers at the locations of those friendly soldiers and set its targetname the same as the trigger_relay. So when its triggered friendly soldiers will vanish and monster_makers will replace them with the hostile soldiers.