Excel can automatically add Group totals by inserting a row in-between, can spreadsheet::writeExcel do it in similar fashion?

No, you'll have to detect the change in column values and write the subtotal rows yourself. The library won't execute macros for you.

Thanks for your response. I am actually trying to program a generic Excel reporting module which (for now) does not know how many columns/rows it will have to write to Excel and will not know what columns it should group with.
Any suggestions on any other perl lib which could run excel macros if I could programatically tell it which column(s) it should use while grouping..
(At this time I am not aware if the macro commands could be lined up for future execution when the excel file is opened)

Any suggestions on any other perl lib which could run excel macros..

Win32::OLE perhaps...if you are running on Windows, and have Excel installed. But really, as you are creating a report, you should know which columns to group by, and which columns to subtotal. Even Excel asks you to confirm if it has guessed correctly when you hit the subtotal button. You could write a 'group by'/subtotal 'these' columns subroutine if you want to be generic about it. But then you would have to write the subtotal rows as you are writing the report, because the non-OLE library (AFAIK) cannot 'insert' rows between already written rows.