This could be a feature request. And at the same time, let me clarify that I haven't used XLS writer extensively.
I am wondering whether it is possible to write in to a specific cell or area in excel worksheet rather than write in to a new file or write in to a new worksheet. Let me explain further:
I have used XLS writer or appender to write in to a file or worksheet in columns a thro f. I have some more to write in to the same worksheet. Can I specify that the new data should be written in the columns g thro s?
As fas as I know the XLS Writer creates a new file, while the XLS Sheet Appender creates a new sheet. No way to insert into an existing one.
But of course you can read in your existing sheet, manipulate it in the KNIME Analytics Platform (i.e. use a Column Appender to append G - S to your existing A - F) and replace the existing sheet.
If you want assistance with that please let me know.