There have already been human babies born with modified genetics to make them less susceptible to HIV. And in the realm of other biology where experimentation i

There have already been human babies born with modified genetics to make them less susceptible to HIV. And in the realm of other biology where experimentation is encouraged we've definitely transferred genes for things like frost resistance between organisms. We don't generally make our own genes yet, just break ones we don't want or transfer ones we do want, but if the human race decided to allow it, we could certainly make a good start on improving the body for handling non-Earth conditions.