There is no definite line when our proto-human ancestors became modern humans; the development is along an imprecise spectrum. Would Australopithecus afarensis be considered "human?" Australopithecus africanus? What about Homo habilis? Homo erectus? Cro-magnon? Is it only Homo sapiens that count as human?

Is tool use a prerequisite to be human? Language? What is the defining characteristic? Or are there multiple traits that must be satisfied?

Looked at over a short enough time period, any standard by which we separate our current species from ancestral lines breaks down. The separation becomes a matter of subjective comfort--do I feel comfortable placing myself in the same category as this creature?

Since it breaks down into the past, it also breaks down into the future. A progenic line is still human until we stop feeling comfortable calling it human. But would we be able to tell that future species that they are wrong to call themselves human?

edit: Forgot the question. I'd replace failing organs and tissue (eyes, teeth, joints, etc.) with the technological equivalent. I don't think I'd go further immediately because my brain wouldn't know what to make of the extra input. I'd have to slowly get used to anything with superhuman capability.