My goal is to alter Impossible so that the Geoscape resembles Classic, the enemy HP and accuracy resembles Normal, but the AI and enemy count is like Impossible.
I thought I figured it out when I found and modified DefaultGameCore.ini, changing all the values that I wanted. However, when starting a new Impossible campaign, Sectoids have extra HP and accuracy, something that I specifically removed.
I am on Steam, if that affects anything.