New option 3 is added to System Variable @ISE. When setting it to 3 and import multiple data files to a book with multiple sheet,
no matter the sheet is empty or not, data will be imported to existing sheet first.
Suppose there is a workbook with 3 sheets. There are data in them.
Select 3 other files to import with Multi-file Import mode as Start New Sheet.
Data will be imported to the 3 sheets, instead of creating 3 more sheet and import them.