You won't lose any data with a CTRNAND transfer no. It's not a format.Friend list, streetpasses, etc. Will all of that be retained?
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You can't use the latest versions of Luma unless you install Boot9Strap. v7.0.5 is the "newest" one that will work with your setup. You can update your emunand all you want after you install Luma. Although if you want semi-permanent hax and be able to do away with the Emunand I would install B9S anyway.Are there any major downsides of using Luma V7.0.5 instead of the latest version? Is it still possible to update emunand to the latest firmware?