I don’t plan to make the game’s source code available, and even if I did, I don’t think making it available for the purpose of modding would be wise. SS’s APIs were designed and modified alongside the game itself, so the source code would not necessarily be a good way to learn. On top of that, some stuff is just plain spaghetti code. Hex, for example, is way better in terms of structure and consistency. That said, I wouldn’t be opposed to sharing snippets of game code that I am able to personally annotate or comment on if there are like specific things you want to see, I also am willing to provide direct help and answers on the game’s Discord (or wherever else) to modders to help them get stuff off the ground. Also, the complete source code of the convent mod is available for modders to peruse.
I wanted to see the game's code more as a whole like Monster Girl Dreams mostly because I'm clueless about what specific thing I should be asking for. But if modifying the game's vanilla content is very hard or impossible, I guess I'll just have to see what Convent mod did and try to learn what I can.