Steve,

You are right that meds and other things you take in by mouth will have an effect on your cells.  But, they will generally not change the fundamental way that the cell works or processes information.  

To correct the enzymatic defects in CAH, you would have to get inside the cell and fix the way that that cell works.  I think that is essentially what gene therapy is, something we know is not very easy to achieve. 

What you are describing....i.e. taking in something via mouth in order to produce a desired effect on the cells....is essentially what we are doing when we take in oral glucocorticoids and mineralocorticoids to treat CAH.