Here we go :
1- Use 3DSNUS to download title
0004800F484E4841 in
version 0 and title
0004013800000102 in
version 1489. No spoof = DevMenu and GW. If not, then spoof
version 0 one to a really high number (60250 for example).
2- So I recommend using GW with DevMenu.3ds to install both generated cia directly to SysNAND. (Done then, go to 5)
3- If you don't have DevMenu, BEFORE installing CIAs, first use
FBI (available on this forum too) to uninstall title
0004013800000102 (TWL_FIRM), not sure
BigBlueMenu will be able to uninstall it.
4- Now install both CIAs with
FBI or
BigBlueMenu.
5- Reboot and enjoy
-- EDIT --
Forgot to add that, as
gamesquest1 said, downgrading TWL_FIRM (0004013800000102) on
NEW 3DS with version from
OLD 3DS may cause somme issues so until someone with NAND mod willing to try this out, don't do it, even if it's only affect DS games btw. Whitelist (0004800F484E4841) can be replaced safely on any devices.