Looks like the methods are already there but they’re not streamlined yet, as well as the research. You’d most likely go for an existing virus that targets cell mitochondria specifically, maybe you’d want mitochondria of a specific cell. The viral DNA can be altered in the ways you want and the virus can deliver the DNA to your cells. I’m not sure how specifically this would be done, usually they use viruses to deliver a small portion of a DNA that encodes a specific protein, so the main objective there is to make the cell produce that protein. Not sure how that would work with simply mortifying existing DNA.