Meaning of campaign difficulty levels

[Phasma Felis]

Hello! I just bought the game after fiddling with the demo for a while. In the New Hope campaign, what's the difference between Normal/Oldschool/Hardcore difficulty? Is it possible to change the difficulty once the game starts?

[n9103]

AFAIK, the number or enemies and the size of resources, based on the editor's interface last time I used it (couple major versions ago), but that could have changed. I'd be surprised though, since, for the most part, the campaign is still the same it was back then. The enemy numbers are generally more significant than the resources in the campaigns though, since taking too long means they evolve too far for the tech you can use.

And I'm pretty sure you can't change mid-game.