After saving exported file to your computer with TAB selected as delimiter, rename it from "products.csv" to "products.txt".
Right click on that file and select "Open with..." -> "Choose program" -> "Microsoft Excel".
File will open in Excel, you can modify it, saved it as xls file or save it as TXT file again and import back to your store with changes.
!!! If you decide to import it back, make sure you do database backup before the import in "DB Backup/Restore" menu. Also, we suggest to clean all statistics in "Summary" menu before doing backup as it makes backup file much smaller.