Even in fiction and fantasy, there's a limit to the suspension of disbelief. All games of this type ask us to believe that it's possible for the MC to be sleeping with more than a dozen women at the same time, without consequences, and the in-universe rule that makes that credible, in most cases, is that women love enormous cocks. In this mod, I've had to come up with reasons why each woman wants to have sex with Anon despite him being on the opposite end of the endowment spectrum, and I think it works well enough for our purposes.
I'm hesitant on this suggestion because it takes the already incredible premise that Anon can sleep with any woman in the game, and stretches it so that Eve can also sleep with any woman in the game, making her and every woman in the game at least bisexual or bi-curious. In the case of trans Eve, all of the women also have to be okay with Eve being a woman with a penis, which has definitely not been my own experience.
Yes, anything goes in a porn game, but this is an unusual case. Normal pornography can be largely visual, whereas SPH is about what people say, think, and feel. This mod fails (at least for me) if it's just an image replacement mod, like a hairy mod. People need to acknowledge the MC's lack of size and stamina, so the dialog has to ring true, and the scenarios have to feel believable. I can kind of see trans Eve being willing to have an open relationship so that Anon can still have penis-in-vagina sex, but I would find it difficult to write credible scenarios where Eve was able to convince Anon's lovers to also have sex with her, without him. Anon might be persuasive enough to convince his lovers to let Eve join them -- but then there would be no need for Eve to tell Anon about her conquests, so I'd have to put the threesomes in the game for anyone to know that they were happening.
I don't think I can make this one work in a way that I could be happy with.