Flashcarts all come from China - you're not allowed to buy from there?
Yes a hardmod could be used. It may or may not help depending on two things, a) if B9S is installed in the backup and b) if the NAND backup is old enough to not have the modification made that causes the home menu to not load without CFW.
I remember that A9LH must be installed in backups because people used to install CFW that way - taking a NAND backup with a hardmod, modifying it, then flashing it back. But is B9S the same? I'm not sure.
If it isn't, then the NAND backup needs to be old enough to not have whatever modification you did that causes the home menu to not load. Otherwise you'll still be in the same situation.
Going to try tagging
@zoogie to answer the question about B9S.... He's a DSiWare expert but hopefully has knowledge across the board?