The process of making and transferring changes is pretty straightforward relatively speaking in an embroyo. You change the DNA of one cell and all the cells now inherit this change.
But let's say that after x amount of years from now on we are capable of creating perfect changes to the DNA of a person. What could the process of transferring this change be for an adult human being? Given that there are about approx. One trillion cells in our body, is it even possible to change it?
I think that using a designed virus could be one way, T4 bacteriophages do a pretty good job of taking over the nuclear material of the bacteria. But I don't think it can be too effective given that most of the viral activity is restricted to the blood. Also I don't think the blood brain barrier let's the viruses across.
Highly speculative topic but I would appreciate any insights on this.