First up, look for header_operations.py, as this is literally like the dictionary for modding M&B. It has all the most important commands in it.
To do what you want to do, you want to go to module_mission_templates.py. The "module" files are the main ones you normally edit. So mission_teamplates is basically covering everything to do with missions, gamemodes, and most importantly triggers. You can check out header_triggers for some triggers you can use, but normally in mission templates you will see something like this:
(1, 0, 0, ,
That is the beginning part of a trigger which fires every 1 second. I put together a quick version of what you probably want, though other people can correct it if i messed something up:
(ti_on_agent_spawn, 0, 0, , #Trigger fires every time an agent spawns. (Found in header_triggers).
(multiplayer_is_server), #Is server
(try_for_players, ":player_no", 1), #Loop through all players on the server
(player_get_agent_id, ":player_agent_id", ":player_no"), #Get player's agent id
(agent_is_alive, ":player_agent_id"), #Check the agent is alive
(agent_set_reload_speed_modifier, ":player_agent_id", 999), #Set reload speed (between 0-1000)
All these commands are found in the header operations file. Anyway, all you have to do then is find the right place to put this piece of code. Look through the mission templates file using the find tool and you should find different gamemodes looking like this:
"multiplayer_bt",mtf_battle_mode,-1, #battle mode
"You lead your men to battle.",
Thats the battle mode section. Somewhere after this bit:
You'll see some triggers. Just splice your code in between one of those, compile the module, and you should be done. Then you just upload you mission_templates.txt file onto your server and it will work in battle mode.
....long reply i know...but hopefully it helps get you started. Check out some of the modding tutorials in these and the taleworlds forums on modding for other stuff. The are really helpful.