Can CRISPR-Cas9 make changes on a living organism?
Answer is yes, but it depends on which kind of phenotype you're going to restore/change. As you can imagine, using crispr cas9 on an high amount of cells require one condition: edited cells need to have a clear advantage in surviving besides the previous. 

Here's an example of a crispr-cas9 protocol followed to restore a wildtype phenotype in adult mice.