Ridge Racer 3D StreetPass Duel Duplication

Edit (2015-12-29): It doesn't have to be this complex.  There's a far simpler method, which I've detailed in a new post.

As mentioned in my previous post, I have discovered a method to duplicate StreetPass duels in Ridge Racer 3D.  In order to do it, you may need an SD card reader, depending on which model of 3DS you have.  It requires a kind of lengthy setup, and as suggested by the previous sentence, involves messing around with data on your SD card, so it's probably not for everyone.

DISCLAIMER: Since these directions involve messing with the extra data on your 3DS' SD card, take extra special care to make sure you're not accidentally doing something silly like deleting data for another game or anything like that.  When followed verbatim, these directions work without adverse side effects.  I'm not responsible for anything that may happen if you don't follow these directions properly.

1. After getting a Ridge Racer 3D StreetPass, fire up Ridge Racer 3D.
2. Go to Single Player → StreetPass Duel, just like usual.
3. Accept your 2000 points per StreetPass.  If a duel is saved to extra data here (there will be a progress bar between the two "Saving..." dialogs), you can proceed past this step.
4. Once the duel is saved to extra data and you're sitting there looking at the list of duels, press HOME and exit the game.
5. (Old 3DS) Turn off your 3DS, remove the SD card, and insert into your SD card reader (which is hopefully attached to your computer).
   (New 3DS) Go to System Settings → Data Management → microSD Management, and get it connected to the network (i.e. if you haven't already set it up, do so now).
6. Browse to one of the following paths, depending on your console's region: (for the New 3DS, go into the microSD directory first)
   NA: Nintendo 3DS\<console-specific hash>\<console-specific hash>\extdata\00000000\00000358\00000000
   EU: Nintendo 3DS\<console-specific hash>\<console-specific hash>\extdata\00000000\0000033B\00000000
   JP: Nintendo 3DS\<console-specific hash>\<console-specific hash>\extdata\00000000\00000328\00000000
7. Copy the files there to a new directory in the root of the SD card.  See the part of the paths in the previous step that's different per region?  I personally recommend putting that number in the name of the directory you're creating.
8. (Old 3DS) Remove the SD card from your SD card reader, put it back in your 3DS, and turn the system back on.
   (New 3DS) Completely exit System Settings.
9. Fire up Ridge Racer 3D again.
10. Beat the duel.  The game will then delete it from extra data, unless of course you hit a duel win milestone and get extra bonus points, in which case, beat the duel again so that the game will delete it from the extra data.

To restore the duel, just copy the data you backed up back to the place where you originally found it, making sure to overwrite when prompted.  The next time you start the game and go into StreetPass Duel, the duel will be there and you can get its points again.  If you're wondering, the numbers that differ per region in the path to the game's extra data are a part of the game's Title ID, which I found here.