No CFW Needed Instructions:
What you need: A 3ds on any firmware version and region, FE: Fates (doesn't matter what version), a homebrew entrypoint, and JK's Save Manager
1. Download the zip attached to this post.
2. If you don't have homebrew set up yet, follow this guide to do so:
http://smealum.github.io/3ds/
3. Download and install this homebrew:
https://gbatemp.net/threads/release-jks-savemanager-homebrew-cia-save-manager.413143/
4. Open the homebrew menu and launch JK's Save Manager.
5. Find your copy of Fire Emblem Fates in the menu that pops up. After selecting it and the save manager loads, select "Extra data options" then "Export". Name the output folder "Release".
6. After it completes, turn off your system, eject the sd card, and put it in your computer (or use microSD management/ftp if you want)
7. Open the "Release" folder on your sd card. Delete any file that begin with g_
8. Open the zip file from this post and navigate to the "Release" folder in the "Non-CFW" folder.
9. Merge the "Release" folder from the zip with the folder on your sd card by copying it to the same location as the "Release" folder on your sd card.
10. Put the sd card back in your 3ds and turn it on (or quit microSD management/ftp)
11. Get to the homebrew menu and launch JK's Save Manager.
12. Navigate to your copy of Fates again.
13. This time, go to Extra Data options and select "Import".
14. Select the backup named "Release" and import it.
15. Wait. This can take some time, so be patient.
16. Congrats! We're almost done. For the next part, you can either get the units by beating my castle (Address is 02149-33009-41650-34669) or moving on to step 17.
17. Download and extract the .exe for this application:
https://gbatemp.net/threads/feftwiddler-fire-emblem-fates-save-editor.422439/
18. Extract the "Unit Files" folder from the zip on this post.
19. Dump your save with JK's Save Manager.
20. Open the save with FEFTwiddler (the program from step 17).
21. Go to the unit tab and click the button in the bottom righthand corner labeled "Import Unit".
22. Select any of the .fef14 files to import.
23. Import as many of the units as you wish, then save the changes.
24. Import your save.
25. Profit.