"System" modifiers are attached to the stellar body afaik, so you'd have to go through considerable trouble to add those anywhere but in the system initializer.I'm interested in having system wide economic effects rather than just planetary and imperial and I'm trying to figure out if that's a possibility.
Also, are jobs that require trade value as an input good possible?
Jobs might have trade value as upkeep, but I'd assume they don't. Adding negative trade value could be easier.