I'm 100% sure that has nothing to see with this, even if this happened after you edited.
Save editing any game can't cause your 3DS to black screen/brick/something like that.
No matter the game nor the save editing tools, since you're only changing individual game files, and not system files.
yeah im not blaming you, but its all strange to me..
youve confirmed ive did the right thing, but hmm i wonder why @@