If you can extract the NK.nbf file, then you can use the XDAtools from this site. Use the OSImage tool to copy the file contents to your XDA flash ROM. I would recommend taking a backup first using the same tool but with the opposit source/destination.
If you still get the error message then you are stuck to the SD card method. Up to my info (didn't try it tho), copying the file through the XDA will not work as the card will be formated during the the copying, you must use a PC reader\writer for this.
You better be very careful as YES there is always possibility to turn your XDA into a very expensive paper weight!! ... but by following the instructions it will go very smoothly.
Good luck ...
HD2 - RSU: 22.214.171.124 - Android: Typhoon 3.5.4