Homebrew Can I basically clone my old 3ds to my new (old) 3ds?

[karikatourea]

And the reason for that is mostly streetpass.
Since homepass is dead (and I miss it) but I still enjoy my 3ds games and even the Mii plaza, I'd like to keep my data in both 3ds.

Can I do this somehow?

 

[KleinesSinchen]

JKSM can backup/restore saves and extdata from system titles.
https://github.com/J-D-K/JKSM/releases
I don’t know how Mii Plaza (and other preinstalled software) reacts when you restore their saves from a different console (e.g. missing data from Mii Maker) as Streetpass Mii Plaza also uses shared extdata.

Before trying to import system saves from another console you should backup your NAND(s).

Whatever you do: NEVER try to restore a NAND-backup from one console on another! Full brick guaranteed.

 

[Ryccardo]

You can do it, backup all three things (save, extdata, spotpass extdata) for Mii Plaza and it will carry over just fine (and if you need the spotpass data for ALL the European dlc puzzles, including the Mario & Happy McDonalds one... just ask!)

Remember: once the green dot on an app's icon disappears, it means that incoming streetpass data has been moved (at the app's discretion) to its save or extdata

Tangentially related, as for your own Miis (CFL_DB in shared extdata F00000B) they will become uneditable without manually editing the system ID; while for the step counter history use the dev app PedometerChanger