"..In any case, how do I go about updating an existing spreadsheet if not with SaveParser? Do I need to instead use both ParseExcel and WriteExcel instead? Can WriteExcel update and existing spreadsheet?.."
To Update an existing Excel sheet Please see MODIFYING AND REWRITING EXCEL FILES
Spreadsheet::ParseExcel::SaveParser module can be used to read and rewrite an Excel file (i.e Rewrite an existing Excel file). Though this module is a wrapper around Spreadsheet::ParseExcel and Spreadsheet::WriteExcel. Spreadsheet::WriteExcel module cannot be used to write to an existing Excel file.
Please check the description of these modules: Spreadsheet::WriteExcel, Spreadsheet::ParseExcel and Spreadsheet::ParseExcel::SaveParser
Hope this helps
If you tell me, I'll forget.
If you show me, I'll remember.
if you involve me, I'll understand.
--- Author unknown to me