I'm not too sure about triggers at the moment, but I know you can change your patrol objective manually by looking at the PatrolObjective file in UPCData\UPCCampaignData, and changing the "PlayerCurrentObjective=ID..." in your saved game.
I like your idea about the increased renown to simulate the shortages. I think that would be the most effective way to go about this, and it should just be a matter of creating more IntervalOptions in the Ammunition.upc
