Was this via gene transfer? Any idea how far off we are from overwriting entire genes with known perfect copies? And if we can do that, then how much longer b

Was this via gene transfer? Any idea how far off we are from overwriting entire genes with known perfect copies? And if we can do that, then how much longer before we can iteratively overwrite segments until we've overwritten the entire genome in every cell with a perfect copy (derived by merging the sequences of many of our mutated cells)?