If they are the same image, why would/should you have to submit them individually? If the first is accepted, then wouldn't the following 999 be accepted as well? Unless you mean you are going for the "Terracotta Warrior" look (hundreds of soldiers all wearing the same uniform but each face different)
Faction NPCs, unless its changed, should be a case of sending image links to the Art Team for approval, for each race. Then once accepted, any NPCs of that race will then have that image available in the Edit NPC page, along with the normal rules images. If the NPC is removed from the faction, it reverts to a rules image.
Edit NPC page seems to not work at the moment, but that was how it was supposed to work.