Just a wild thought: if aliens wanted to change a genome of some species, what are the chances they would construct viruses to do that? AFAIK CRISP uses something similar.
That would probably only work if it gave the altered species a significant advantage (or if you had a system to detect and penalize/eliminate individuals depending on their genome, at scale).
At this point in time, do you really think that viruses are incapable of sweeping the globe and infecting a significant fraction of humanity, if they don't provide a benefit to the host?
The parent was more specific and asked about changing a species's genome. Infecting everyone does not lead to a change in genome if they die (or fight it off).
Assuming a low percent of the infected get their genome changed or produce offspring with altered genome, those don't take over.
