No, this isn't someone who wants to amputate a perfectly functional limb because, in their mind, that's how they should be (Body Integrity Identity Disorder).
No, "transabled" are people on tumblr who, despite not having any loss of function or medically diagnosed disability, self-identify as physically disabled. Hence the "trans". And if you tell them you consider that to be bullshit, they label you as being "transphobic".
Alright, I'm not exactly an expert on trans/cis spectrum, I'm not a psychologist or psychiatrist, I know there's a lot I don't know about the human condition. But fucking really? For fuck's sake, really?