Comment by echelon

You mean cancer.

Or a wicked disease state like Huntington's that causes your DNA to slip.

Simple failures with catostrophic outcomes are much more likely than rewiring and restarting all of the developmental program across huge cell and tissue populations.

It would be more likely to grow transplant tissue exogenously. It's far safer than using the body as a test tube.

These gene editing techniques are used to fix simple (typically one cause) genetic diseases. Not reengineer live organisms "in flight".