3DS System Settings Mod

Making your own wallpaper

Open godmode9 (hold start while booting)
Go to CTRNAND, titles, 00040010, 0002X000 (X can be any number), content and select the .tmd file
Select "TMD file options" and "mount cxi/nds image to drive" then press A
Open the romfs folder
Highlight the base_LZ.bin file and press Y to copy it
Press B two times to go to the main menu
Go to SDCARD then press Y again to paste it
Power off and insert the sdcard on your computer then copy the base_LZ.bin file on the folder you're doing the mod on

Let's start by opening the bg_white - template.bclim file on kukkii and export it to PNG
Edit the image and import it through kukkii, then save it (ctrl + s is your friend :p)
Now the image file is done, you have to put it on the archive so first, open karameru
Go to Tools > Compression > Nintendo > Decompress > General just like the image below
Open the base_LZ.bin file you previously extracted on godmode9 and save the uncompressed file
Open the uncompressed base_LZ file, go to "timg", click "bg_white.bclim" on the file list and press the "replace file" button
Replace it with the edited background (bg_white - template.bclim)
Right click on blyt folder and select replace blyt
Select the folder you put the top and bottom screen layouts in (those files are important as they resize the wallpaper and remove the yellow gradient)
Save the changes (again, ctrl+s is your friend)
Go to Tools > Compression > Nintendo > Compress > LZ10
Replace the base_LZ.bin file while compressing, the file should now be modded with your modifications

In your sdcard, go to luma/titles and create a folder named the following depending of your region:
- 0004001000022000 for Europe
- 0004001000021000 for USA
- 0004001000020000 for Japan
Create a "romfs" folder inside and put your base_LZ.bin file inside

(A valid path for Europe would be luma/titles/0004001000022000/romfs/base_LZ.bin)
Don't forget to enable game patching on luma config (hold select while booting)
Enjoy!