If you call xlswrite(), I believe it will overwrite the data (that is, replace existing cells with new data and add any new ones to blank cells), right?
If you want to replace the whole workbook (not overwrite it), delete it before calling xlswrite().
If you want to add additional data into new worksheets in the workbook, then specify a new worksheet name in the argument list of xlswrite(). Use xlsinfo() to get existing sheet names.
