Yes, you may edit the models provided you are using the right software for your purpose. Popular mesh-modeling softwares such as Blender, ZBrush, Meshmixer, Sketchup, Meshlab, etc. may serve your purpose for editing the mesh. However, you should avoid using CAD softwares for editing of STL files (or any other polygonal mesh models) as they are not the right tools for this application.
If we know the end-use application of your project, we can deliver the 3D models as per your needs, so as to save you time.
