You can't add a Thing from a script. In this case you need to bootstrap and add a
bootstrap condition.
Because each game system is custom created no list of every field and tag exists.
I would recommend reading the
Glossary of Terms for the Editor. Then check out
FAQ#2 for all the places to learn about the editor including YouTube videos. Welcome to the wonderful world of using the HL editor which will be the most frustrating and rewarding thing you can do with Hero Lab.