Due to seedminer being the current exploit method, it is easier to perform a System Transfer before setting up custom firmware on the target console. Dumping the source console's movable.sed before performing the transfer means that seedminer can be bypassed entirely on the target console after.
If the target console does already has CFW, follow this guide instead.
What You Need
The latest release of GodMode9 (the GodMode9 .zip file)
Instructions
Section I - Prep Work
For the source console only, perform the following steps:
Power off your device
Insert your SD card into your computer
Copy GodMode9.firm from the GodMode9 .zip to the /luma/payloads/ folder on your SD card
Copy the gm9 folder from the GodMode9 .zip to the root of your SD card
Reinsert your SD card into your device
Section II - NAND Backup and movable.sed
Press and hold Start, and while holding Start, power on your device. This will launch GodMode9
Press Home to bring up the action menu
Select "Scripts..."
Select "GM9Megascript"
Select "Dump Options"
Select "System File Dump Options"
Select "Dump movable.sed"
Press A to confirm
Press A to continue
Press B twice to return to the main menu
Select "Backup Options"
Select "SysNAND Backup"
Press A to confirm
This process will take some time
If you get an error, make sure that you have at least 1.3GB of free space on your SD card
Press A to continue
Press B to return to the main menu
Select "Exit"
Press A to relock write permissions if prompted
Press and hold R, then press Start to power off your device
Insert your SD card into your computer
Copy <date>_<serialnumber>_sysnand_00.bin, <date>_<serialnumber>_sysnand_00.bin.sha, and <serialnumber>_movable_00.sed> from /gm9/out to a safe place on your computer, then delete the .bin and .bin.sha files from the SD card
Reinsert your SD card into your device
The above files should be kept safe, preferably in multiple locations. Use the movable.sed for tools like PicHaxx Injector or unSAFE_MODE Exploit Injector.
Section III - System Transfer
Perform the system transfer as usual. If at all possible, choose a "PC-Based Transfer".
If you cannot follow a PC-Based Transfer and must instead use a Wireless Transfer, be aware that with this method, homebrew software, cartridge dumps, and any other data only obtainable with CFW will not be transferred over. If you choose a Wireless Transfer anyway, you will need to take extra steps to move over the lost data. Select "Do not delete" during the transfer to preserve all data on the source system, or else you will have to reobtain all lost data again by hand.
Next Steps - Branching of the Way
Were you able to perform a PC-Based Transfer in Section III?
The source console is finished. The following pages should only be performed on the target console.
After CFW is installed, place faketik on the console's SD card. After this, once you finish Section IV of Finalizing Setup, run faketik before opening FBI. This will restore all homebrew applications that disappeared after the transfer.
This section is a work in progress. Notes:
Provide more detailed instructions on how to use ninfs.
Continue to BannerBomb3, but return here immediately after CFW is installed
If you were not able to perform a PC-Based Transfer, you will want to manually restore all the homebrew data after CFW is installed but before following Finalizing Setup.
To do this, do the following:
Copy all folders other than Nintendo 3DS and DCIM from the source console's SD card onto the target console's SD card.
Insert the source console's SD card into your PC, mount its Nintendo 3DS folder using ninfs, and copy out all games/savedata that was not transferred onto the target console.
Unmount the source console, mount the target console in ninfs, and copy all obtained games/savedata into the target console'sNintendo 3DS folder.
Rebuild title.db on the target console to force all the new games/savedata to appear.