public bool ExportDWGModifyLayerTable(Document document, View view)
{
    bool exported = false;
    IList<string> setupNames = BaseExportOptions.GetPredefinedSetupNames(document);
    if (setupNames.Count > 0)
    {
        // Get the export options for the first predefined setup
        DWGExportOptions dwgOptions = DWGExportOptions.GetPredefinedOptions(document, setupNames[0]);

        // Get the export layer table
        ExportLayerTable layerTable = dwgOptions.GetExportLayerTable();

        // Find the first mapping for the Ceilings category
        string category = "Ceilings";
        ExportLayerKey targetKey = layerTable.GetKeys().First<ExportLayerKey>(layerKey => layerKey.CategoryName == category);
        ExportLayerInfo targetInfo = layerTable[targetKey];

        // change the color name and cut color number for this mapping
        targetInfo.ColorName = "31";
        targetInfo.CutColorNumber = 31;

        // Set the change back to the map
        layerTable[targetKey] = targetInfo;

        // Set the modified table back to the options
        dwgOptions.SetExportLayerTable(layerTable);

        ICollection<ElementId> views = new List<ElementId>();
        views.Add(view.Id);

        exported = document.Export(Path.GetDirectoryName(document.PathName),
            Path.GetFileNameWithoutExtension(document.PathName), views, dwgOptions);
    }

    return exported;
}

Public Function ExportDWGModifyLayerTable(document As Document, view As View) As Boolean
   Dim exported As Boolean = False
   Dim setupNames As IList(Of String) = BaseExportOptions.GetPredefinedSetupNames(document)
   If setupNames.Count > 0 Then
      ' Get the export options for the first predefined setup
      Dim dwgOptions As DWGExportOptions = DWGExportOptions.GetPredefinedOptions(document, setupNames(0))

      ' Get the export layer table
      Dim layerTable As ExportLayerTable = dwgOptions.GetExportLayerTable()

      ' Find the first mapping for the Ceilings category
      Dim category As String = "Ceilings"
      Dim targetKey As ExportLayerKey = layerTable.GetKeys().First(Function(layerKey) layerKey.CategoryName = category)
      Dim targetInfo As ExportLayerInfo = layerTable(targetKey)

      ' change the color name and cut color number for this mapping
      targetInfo.ColorName = "31"
      targetInfo.CutColorNumber = 31

      ' Set the change back to the map
      layerTable(targetKey) = targetInfo

      ' Set the modified table back to the options
      dwgOptions.SetExportLayerTable(layerTable)

      Dim views As ICollection(Of ElementId) = New List(Of ElementId)()
      views.Add(view.Id)

      exported = document.Export(Path.GetDirectoryName(document.PathName), Path.GetFileNameWithoutExtension(document.PathName), views, dwgOptions)
   End If

   Return exported
End Function