This is a great question. When we, humans, think of changing ourselves, we typically think of education, which is essentially reprogramming: changing laws, society structure, economy and things of this sort. Many aliens would think of genetic modification.
Currently, humanity is opposed to genetic modification. I would say very few people, maybe one in many thousands would be open to the idea of genetic modification. This small layer of people would include experts in genetics, people with genetic disorders and human-alien hybrids aware of their hybrid nature. There are very few of this kind. Even most genetics experts are not open to the idea of genetic modification.
Most of this fear comes from a very proper judgment that with current humanity's morale, the genetic modification done by humans will be immoral. Since our mainstream is hijacked by the negative MIC, we correctly reason that allowing for genetic modification of humans would result in misuse of this powerful technology. For example, MIC officials would modify their offspring to make them more powerful deceivers and more efficient leaders of MIC. MIC would also want to create genetically modified slaves and warriors. MIC already is succeeding in creating and programming assassins for terrorist attacks. The mind-controlled soldiers and terrorists are programmed by MIC using a combination of pharmaceuticals, electromagnetics and in-person training. Unleashing genetic manipulation would make things worse.
Obviously, humanity is not ready for genetic modification by the aliens either. The discovery of the genetic manipulation program of the greys is already making people feel uneasy. Most influential are the books and lectures of David Michael Jacobs. Prof. Jacobs correctly demonstrates that from a human perspective, the hybridizations were completely wrong. They were secret, harming both the abductees and the hybrids created by the greys, which were modified in ways humans would not approve. Besides, the humans suspect the greys in the attempt of hijacking our system and taking control. It is a dominant theme of this book and the dominant theme of humanity that the control is almost always hijacked, so the humans suspect the aliens in hijacking the control as the humans suspect anyone, especially foreigners in hijacking the control. Part of anti-Jewish sentiment in human culture is the ability of Jews to hijack the control of countries. I align strongly with Jewish culture and understand how this hijacking by the Jews is happening and how it can negatively influence the hijacked countries. Most importantly the people of hijacked countries feel alienated from their leadership and as you know, this diminishes their cooperation and motivation for labor.
So the take-home message is that humans disapprove of genetic modification especially by aliens because they are suspicious of the motives and suspect the attempt of hijacking the control of the society.
There are indications that aliens use hybrids for monitoring human society and secretly manipulating humanity's affairs. From the human perspective, this is one of the steps towards hijacking control.
I also need to comment that Bashar a few years ago indicated that it is almost certain that there are secret projects run by humans that are already doing human cloning and that maybe already now, there are human-made human clones walking among us. I would not be surprised.
MIC = military-industrial complex