Ultimately the extension comes down to a single function, room_pack_load_map. It has a few convenience versions (like loading from a string or from a file instead) and some functions to control the behaviour (like pushing freshly loaded items to a list so that you can keep track of them, or not loading specific types of content), but at core you call the function and it inserts the contents of a room at given position. Deciding when to call and what data to pass in is up to you.
I can look into making a tutorial or two when the work projects stop being on fire.