"Ok, well can we use viruses to trigger certain mutations?"
Integration of viral DNA into the host genome is a sort of mutation.
Any retrovirus can alter gene expression, simply by integrating into a crucial spot in the host genome (e.g., a promoter or exon site).
So far it's not possible to direct the site of insertion in humans. It can be done in mice, but requires the experimenter to start with mice that are already genetically modified (with loxP sites flanking the region to be altered, and Cre recombinase expression present in the tissue of interest).