First, I see the author has made a new module Excel::Writer::XLSX to replace the deprecated Spreadsheet::WriteExcelXML.

I would use separate reading and writing processes. First save the current file as a new, temp name. Read it to get data into suitable form. Write the new file updated as desired. Save the new, updated file. The clear separation should help maintenance of your code.

I have used Excel readers and writers a lot but am not aware of any that can read and write the same stream, but then I have never needed an update capability either.