The windows 10 iso can simply be extracted to a FAT32 formatted USB thumbdrive to be used for clean install. How can a clean install, performed correctly (boot from the USB/DVD and deleting/formatting the existing windows and system partition(s)) result in a state of "if it never ran the fresh install"? After the partitions are deleted during initial setup you won't ever get back to the previously running windows. When you don't know how to clean install windows manually, try the "resetpc" option or the "start fresh" option.