I think the main question, if this were to be considered, is how integrated has each girl made their disability into their lifestyle? In other words, how easily could they adapt to normality, considering the abnormal circumstances they currently reside and thrive in? Just going down the list from the characters page, here's what I'm thinking.
Emi is at the peak of her career as a track star thanks to her accident. For her, her current prosthetic limbs simply give her feet. She still has her knees and can walk as fluidly as any other person with actual legs. Her only difference is that she doesn't have the ability to feel terrain by the placement of her foot due to the lack of nerves in that part of her body. If anything, her current prosthetic limbs are more efficient (I would imagine) due to the fact that she has one less movable joint - her ankles. She could potentially swing either way on this, though I would imagine she would choose not to. She is (most likely) not going to gain any nerves in her feet through advanced prosthetics, and her current limbs works perfectly fine as is. If she truly wanted to look normal, a simple flesh cast that fits over her current limbs could probably be adapted, as well as shoes. Her prosthetics wouldn't need to be changed; just camouflaged. Again, I'd imagine she'd opt not to.
Like G3n0c1de said earlier, Hanako's issues are more emotional and mental then they are physical. She now has a scar that stands out heavily against the rest of her body, and she is embarrassed about it. Whether new skin would solve this problem is hard to say, but considering that she has lived with these scars and in her current reclusive lifestyle for years (her accident occurred while she was young), fixing the problem would probably not solve the emotional and mental scaring she has let grow. So long as people can look past the scaring and see Hanako for herself, she'll be fine. That being said, whether Hanako takes the prosthetic skin or not would more likely be dependent on the opinion of her friends, Lilly and Hisao (assuming this comes up on her path). Lilly would probably say that it makes no difference to her (seeing as she can't see) and that Hanako should do what she thinks is right. Hisao would probably try to convince her otherwise and not take it, taking the role of the "love you but don't 'love you' love you" friend, saying that she doesn't need the skin to be herself and make friends, but would probably also leave it up to Hanako in the end.
Lilly, being blind from birth, has likely grown up with imaginations of what things look like. She has learned to live with her disability, and I imagine that by giving her sight, she would be put through far more hardships than she would be by living her life blind. She would have to learn to recognize faces, get colors straight (her red could be our blue), and then there's all the other concepts that require visual cognizance. However, from what I've seen of Lilly, I'm sure she's suppressing her resentment for having to rely on people for help (such as the Shopping trip). Given the option, I'm sure that this resentment would come out, and it would become an argument between her and her friends of "I don't want to be a burden on you," versus "But you're not a burden on us." I really couldn't predict either way whether she would or she wouldn't take them.
Rin has become very skilled as using her feet to do everyday things. Her lack of arms also gives her the ability to be generally lazy, as noted by the loafing around at the school festival, since she can't be expected to perform everything. Giving Rin arms would probably be the equivalent of amputating someone's dominant hand, skill-set wise. Rin would have to learn to write and do other things with her hands, when all her life, she's been foot-handed. I'm sure everyone's gotten curious and tried to write or do something with their off-hand, so I'm sure they know the difficulty. Our brains learn the most while we're young, so not only will Rin have to learn how to do stuff with her hands, but she's at an age where imprinting that knowledge would be difficult. Besides, I doubt she's want to give up her ability to be lazy. I'd imagine no.
Shizune is both mute and deaf. She can't hear, nor can she speak. Assuming that this was a birth defect, it means she doesn't know (most likely) any phonetics, which means she'd have to learn vocal languages. She'd have all the time in the world, I'm sure, but she'd still have to. However, with Misha at her side, she's never in need of ears or her mouth. Her hands do all the work for her. Misha, so far as we can tell, doesn't mind being a translator and I'm sure Shizune is aware of this. While I'm sure she'd love to stop being a burden, since she is unable to, she might as well make the most of her life with the help of her friends. I still put this as a toss-up however, and lean more towards her actually getting the implants. She's a smart girl and could pick up vocal language quickly. It simply comes down to a case of how overwhelmed will she be from all the sounds she can now hear?
Change is hard. The girls in this story encompass a wide variety of disabilities that they've adapted to for years. If they were given a free ticket to a normal body, I'd envision the more practical girls like Shizune, Lilly, and Emi (only because she was normal once and bawwing about her handicap is bound to come up in the story) accepting them. They don't suffer from identity crisis with their disability, but make the most while having them.
Acknowledging your comment, I'm not sure the identity crisis would be the only considering factor, or the fact that would make this an automatic decision. Lilly would have to be slightly concerned about how she would start getting along with people being able to see their disabilities, the exact reason why Hanako makes perfect friends with her. Emi has gained superior track skills as a result of her losing her legs, and I doubt she'd want to risk it by getting them back.
Hanako would take synthetic skin in a heart-beat. No question. Her disability is her self-esteem shot to shit by her scars. Being seen is torture to her.
And as I said before, she has grown up and gotten into the habit of hiding and not being seen. I know how she feels (somewhat). I'm 19, obese, and have always been the 'new kid' at school since I was never at the same school for more than 2 years (lots of moving). I never got a chance to make and friends, and the fact that my first encounters were almost always the standard new kid taunting comboed with the fat kid insults, I became a recluse, picking up few friends throughout my years. Just by losing weight, which was the physical taunting factor, I doubt I could overcome my reclusiveness in a heart beat because I've grown up with those habits. I can really only express myself like I am right now because the internet gives me the same veil of comfort that Hanako gets with Lilly. You all can't see what I look like, so I'm more able to talk freely.
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Gah! Wall of text on my first post!
