Backup your game, unless you want to redownload it when you want to reset it.
The files go into data/Mission. Do not put them into the Briefing Folder!
Rename the Starter Mod of your choice. For Example:
Kendal Knows HolyE1100.stg > E1100.stg

Instead of 100 Troop Versions, this has the normal and Black Knights at their original Troop size.