Anyhow, it's a deeper subject than I can deal with, but two aspects strike me:
- it's highly likely that benefits from such things will not be equally divided: as usual the rich will get richer (taller, smarter, less disease-ridden, whatever) and the poor won't.
- our discomfort with some of the modifications tends to be higher at the margins.
- before you undertake any modification, determine whether the result will push the existing bounds of normal human capability. We don't make a society of Einsteins.
- in undertaking any modification, consciously try to counter the "golden rule" (i.e. the rich get richer).