title: How do I modify mesh attributes to send custom information in Blender?
body: <p>I have a mesh in 3DS format. I imported this mesh to blender and now, I want to export this mesh back to 3DS but, I want to associate a number (say <code>id</code>) with each vertex of this mesh. Now, I only need the x, y and z coordinates of this newly exported 3DS, and I don't really care about the normals or the texture coordinates. </p>
  
  <p>So the way of keeping the IDs intact could be to insert that number in an un-required attribute, let's say the x coordinate of each vertex normal or the first texture coordinate of each vertex.</p>
  
  <p>Here's what I tried with normals:</p>
  
  <pre><code>import bpy
  import bmesh
  
  object_reference = bpy.context.active_object
  bm = bmesh.new()
  bm.from_mesh(object_reference.data)
  
  for vert in bm.verts:
      vert.normal[0] = vert.index
  
  bm.to_mesh(object_reference.data)
  </code></pre>
  
  <p>But, the normals reverted back to default on export. So, how do I do this?<br>
  I couldn't figure out a way to set the texture coordinates, how can I do so? If I can't, then how can I make the vertex normal hack work? Is there a less-hacky way of doing this?</p>