I've been asked about modding frequently enough elsewhere that it's worth setting my position down here. For the attention-challenged, the short version is this: attribute FC to me and link back to this blog when possible; let me know what you're up to; please respect the exclusion of underage content; wait for 1.0 or suffer; otherwise, mod at will.
The idea that people would be interested in modding a game of mine would have been pretty inconceivable to me three months ago, and is really exciting to me now. As far as I know, Twine games are inherently open source. Even if I wanted to restrict modding, there's no way for a Twine author to do so that I'm aware of. If you're interested in modding FC or seeing my novice coding, open the .html in Twine, which is easy and free. It's that simple. I've had to do some pretty questionable stuff to get to where I wanted to go, and the code is almost completely comment-free since I never meant it to be seen. If anything isn't clear, email me and I'll explain.
Since I have no ability to control modding, my one hesitation has to be a request, not a demand. It's this: please respect the underage content restriction. Here's why. I like FC; I like writing it, coding it, and playing it, and I like seeing others enjoy it too. I'm doing this for fun. Even after 1.0 I intend to keep adding scenes to the game at a reduced rate for a long, long time. So, please leave FC's author appeal intact so I can keep doing that.
There are two things you can do to make my life easier. First, attribute FC to me, please, and backlink to here where you can. It's courtesy, and it will get people with questions about the base game to where they need to go. Second, let me know what you're up to! If your desired changes are small, I may just make them. If not, it's still fun for me to hear. Two notes of caution. First, I am new to coding, and I'm self-taught. That means FC's code is an inhospitable place, full of fierce, misshapen monsters. Second, I'm actively developing FC. I may ruin your work by completely changing things. I've had to completely recode the event system twice now, and stats change with every update. Unless you're happy to update as fast as I do, I'd wait for 1.0.
Finally, I'll link to good mods. In fact, I'd consider including good mods in the game, or making simple code accommodations for them. Several would-be modders have contacted me with plans for simple stat changes – unsurprisingly the TFGames stalwarts want more perfect MtF transitions – and once things stabilize, these could even be included as alternative start options.