They are probably just using something likeExpecting someone to complete games like this is wishful thinking. It doesn't really matter how smart you are, how good at coding you are, or how well you can render. These models don't just apparate out of the ether. They had to be purchased/stolen, made by hand, or a combination of both as most people will typically purchase models and then customize them. In this case, they were most definitely customized because you won't find many female models with penises attached by default.
The game files don't include any of this stuff. It's just rendered images. Short of contacting the dev personally and getting their permission and the files, no one is going to continue the game.
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which is just a geometry shell that goes over your Genesis 3 Female (I believe there's also one for G38 too). So it's possible that no modification were used. In any case you typically can go most of the way there by just finding the texture and the hair assets. That being said I doubt someone will do it because rendering is still a lot of time consuming work and you have to really want to do it.