I think that you would need the original mesh from the asset creator to do this. Depending on what you want to do it may be possible to make additions to a mesh by attaching your own meshes to attachment points added with PEVs Attachment Maker.
It's also note mentioning that if somehow you would be able to reverse-enginner the mesh, it be illegal to do so. My best advise is to learn blender to make your own content, and to make mesh add on's for pre-existing loco's.
