Nintendo recently released a Free To Play game called Nintendo Badge Arcade, the game lets you win some badges, you can add them to the home screen of your 3DS and create your own unique theme, the only problem is is that it has Micro Transaction where you have to spend money to get some of the badges.
Thanks to MrCheeze you can add your own custom badges to your home screen, without the need of Nintendo's game, here is a quote from the source:
Super simple custom badge homebrew for the 3DS. Just add the badges you want as 64x64 PNGs in the badges folder, and run the homebrew to transfer them to your home menu.
Note that GYTB does not work in tandem with Nintendo's Badge Arcade: each will overwrite the badges of the other.
Running Badge Arcade to set up the extdata is also not required, so players stuck without eShop access should still be able to use this normally. However, a firmware of 9.? or above is still necessary
You can get some custom badges from here