Hi!
I think what you want to do is to add element-wise data to the mesh, right? We store element data in separate vectors, which can be in binary (.igb) or text format (.dat extension).
You can use the "collect" feature of meshtool to integrate nodal and element-wise datasets into one single VTK file.
If you let us know what you want to do, we can give you more specific pointers on how to proceed.
Best wishes, Aurel