Editing the mesh of a prefab

How would I go about editing the mesh of a prefab? MeshFilter.mesh is not allowed. MeshFilter.sharedMesh is not plausible because I dont want every mesh being edited.
e.g. I have a prefab that is a sphere with a material. I want to apply Perlin noise to that mesh. However, I dont want any other sphere in the scene being affected.

Might not be the best for everyone but Instead I just create a new GameObject as opposed to a prefab, with CreatePrimitive