I think much of the current research (in adults) is to take viruses, some of which are good at adding DNA to cells, and using them to transport new genetic material to cells. The original genes are usually left intact. In many cases a specific organ may be targeted.
Genetic manipulation of an oocyte may be different. However, it would be a daunting task to select individual genes for modification. And, the pretty pictures of chromosomes are only made during cellular division, so adding and subtracting individual chromosomes is difficult.
If one messes up the genetic makeup of the reproductive organs, the testes or ovaries, then future generations could be put at risk.
Bone marrow transfusions are used to treat leukemia, and are a brutal, dangerous procedure that normally involves killing one's existing bone marrow, and infusing marrow stem cells from a donor. It can change the genetic makeup of the blood including changing one's blood type, but not of the body as a whole.