I got my start in programming by hacking Twine games. This... is not really a Twine game anymore. You can give it a try, though I will warn you that if what you're trying to do is change how the visuals work, it will be a very tedious process in a tangle of an SVG. I could probably say more if I knew what you were going to suggest.
It's probably possible, but you would need to have some very specific knowledge of how the SVG works- not to mention the original fox file. Giving some variation to the foxes is in the plan, actually, though it's been pushed down in favor of bugfixing the visuals.
While I'm passive towards hip/ass content, I much prefer hyperspecialization in what I make. A character with massive boobs and a massive ass is kind of just... middling, to me. Boobs no larger than the ass, ass no larger than the boobs. Those two are the only things I can focus on, so I lose the ability to consider the massive difference in scale between the fox herself and the tits.
You're free to take a crack at it, but it's going to be a long, painful journey. Especially if you don't know how bezier curves are made, both through javascript and through mathematics. I use actual calculus in a few places here.