It isn't quite like modifying your own genes. It's a modified virus that attacks specific cells, so in a sense the "gene therapy" was in modifying the virus and to then insert two breaks in HSV-1's DNA that causes it to fall apart.

Think of it like injecting you with an "infection" that only attacks another infection you don't want. A lot of progress is already being made in this regard with respect to various cancer cells. Of course safety will be paramount in approval. I've no doubt one of the requirements will necessarily be that the deactivated virus have both a very short lifespan, and readily killed with additional injections. Perhaps some kind of trigger could be developed that, when encountering an otherwise harmless tracer chemical or some other safe thing, causes the virus to reliably self-destruct.