var
  Columns: TDBGridColumns;
begin
  Columns := TDBGridColumns.Create(DBGrid1, TColumn);
  try
    Columns.Assign(DBGrid1.Columns);
    try
      { re-assign DB grid's data source }
    finally
      DBGrid1.Columns.Assign(Columns);
    end;
  finally
    Columns.Free;
  end;
end;