I've heard that if you use the Expansion prefix for AI scripts it will use brood war units, but I cannot get it to work for Terran on the map I'm making. I'm running Expansion Terran Campaign Insane and it seems to run the basic SC AI campaign script. Am I doing something wrong? How do I get the AI to make brood war units?

Choose an AI Script originally used by a UED entity in the campaigns, modify an existing script, or write your own. The latter two methods require modding.

"Expansion" scripts are lazily done. They'll research brood war tech, but Expansion Terran Insane won't build medics, and only build valkyries in response to air attacks. Similar deal with the rest of the expansion scripts.