I edited the graphics of a SMM clone, it had the option to change graphics as projects with copyrighted material will be taken down, i cannot give you the publickey as it would get taken down, very sorry.
He would have to supply it via Petit Modem or another way to transfer straight from PC-3DS because since Nintendo owns those sprite sheets and games, they have the right to be able to take down this remake of Mario Maker SB.
You can just use SBFM or smileBasic file manager for homebrew. It's way better than petit modem and there's no sound and its simple to do! To know where to find this, go to smileBasicsource.
Welp, you can't do it on the latest update anyways.... Also with the basic homebrew you can't do anything bad to your 3ds. Duh. So just change the sprites and background, its not that difficult.
Ninty? Just say nintendo. Also Its not pirating unless you do that type of stuff... Homebrew only makes applications/programs much easier to use. Like smileBASIC's SmileBasic File Manager. You can transfer files from PC to SB and vice versa! Homebrew is useful if you make it to.
Miiverse isn't really the best place to talk about Homebrew or that kind of other stuff(let's say that Nintendo doesn't really appreciate the idea of running nonnative code on your Nintendo 3DS)