You will need to edit the scripts to make new scripts to order the AI to build the new units.
The scripts are found in the game's folder > data > scripts > SkirmishScripts.scb
They take some time to load into worldbuilder depending on your device.
I've never edited the AI to build new units but have you tried keeping the original commandbuttons/commansets and just let the AI build the new units through them? While keeping the original prerequisites, too.
Originally Posted by: UTD^Force