Best way is to come chat with us and ask what you want to do, or how to do something: https://github.com/cosmo-ray/Sukeban#chat-with-us
Otherwise, if you want to modify a map, you need tiled A lot of game data, are write in json, so if you want for examples modify a dialogue, the best is to modify it directly, and look how other dialogues do it.
The game code is mostly in lua.
The game engine is here
Issue, and PR are of course open, to write whatever you want in it that concern the game.