Manipulate skinned mesh?

I need to manipulate the vertex of a skinned mesh, but not its sharedMesh (beacuse it remain deformed also when i stop the game). How i can do?

Copy the mesh on startup, so that you're operating on the clone instead:

void Start() {
  Mesh oldMesh = GetComponent<SkinnedMeshRenderer>().sharedMesh;
  Mesh newMesh = (Mesh)Object.Instantiate(oldMesh);
  GetComponent<SkinnedMeshRenderer>().sharedMesh = newMesh;
}