Hi, Ripcord!
I'm glad that you've insterested in this tool. I've worked on it, so may be I can help.
Now you can't add some triggers there. Because most of triggers are depends of current zones, groups, units or terrain, so they depends of current mission.
But we can add some more common triggers, like "coalition kills more", "coalitions units count less", "playing time more" and use them in generator.
Now you can change current set of nodes and templates. Please see special tool for it's in MissionEditor->Generator->nodes, templates menu. Your changed files would be placed in Config/MissionEditor/ directory (not in MISSIONGENERATOR/GENERATORDATA).
Also you can add new unit groups and formations in generator by changing "others.lua".