Format and content of exported file can be controlled at 2 levels.
Please check the API for details of these common options and parameters.
ui.Export in column.render
This is available for Excel export only.
Any customization which is not possible through options and parameters alone
it opens up lot of possibilities like combining of multiple worksheets, add custom content,
formatting to any cell.
In order to do this, you need to understand the
structure of workbook.