If you are able to acquire and isolate what you're trying to copy. How would you go about recreating smallpox, or a synthetic virus engineered to only affect a

If you are able to acquire and isolate what you're trying to copy. How would you go about recreating smallpox, or a synthetic virus engineered to only affect a specific ethnicity? Conversely, if you're interested in a common pathogen, why bother sequencing it?