We used to do such things with breeding programs aimed at improving species for our benefit. Part and parcel of domestication is that there is some control over the nature and quality of the output. That may be inherently limited to natural variation, but seems to work, although breeding out some traits may inadvertently lead to bloodlines which have other specific problems. We see this with dogs, where breeds have specific weaknesses and strengths, some of which would not survive without human intervention. But to run willy-nilly through the genetic code of an organism modifying it to produce something different sounds like the stuff of SciFi/horror and could conceivably produce nonsustainable bloodlines.
At the root of it all is that after 4.6 billion years of climate change (giver or take a few million), do these people really thing they are going to halt that natural dynamic process in its tracks? That alone would certify them as nutcases.
