It's still not completely clear but I assume you want to add a footer and header to your column. You can use a box or cylinder to do that: make them bigger than your column and place them at the correct position so the they span outside the column. The footer at elevation 0 of course and the header elevated to wall-height-header-height. Of course you can create any fancy footer and/or header but the process remains the same.

You can select all parts of your column and export them. After import you have your column+header+footer as a single 3D model.

If you want to change the material names you can get a how-to here:
Change_Material_Names.pdf
Change_Material_Names_files.zip