Three things -
1. Is the body already painted? If so, consider filing or sanding just the very tiniest bit off the edge of the insert holes so you will be less likely to make the finish bubble or flake. I forced in an string ferrule in a painted body and despite not having struck or even touched the body, it created the a tiny bubble under the paint.
2. If you have access to a a sufficiently deep-throated arbor press (get your mind out of the gutter) or a drill press you can do this with much less risk of blemishing the body than by pounding. You could also use a deep clamp with a cushioned caul to protect the body.
3. If you must use a hammer, use a deadblow hammer to reduce the likelihood of your hammer bouncing and then blemishing your body.