there are 2 ways to add troops to a scene, though I have only gotten one of them to work. Unfortunately, it's the (I would say) suckier way (no offense to those that use it, I will explain my opinion) that I got working....
the way that I can get to work is using the operation (spawn_agent,<troopID>),. First you would need to use the operation (set_spawn_position, <pos>),. This works great except that each troop spawned is identical. Doesn't matter what variety of weapons, armor, face codes, etc. you use, they all look the same. This is why (imho) it's suckier.
the other way is to use the operation (add_visitors_to_current_scene,<entry point>,<troopID>,<number of troops>),. This is what is used in the melee fights. You notice there that troops (and their gear) is randomized. I'm not sure what I am missing to get this operation working. I even added the line (modify_visitors_at_site,<sceneID>), but that didn't help.
But there you go. Just have something trigger the operation you want to use.