The game cart is used in conjunction with the premade Ninjhax save game file to load homebrew *.3DS software.
From that point however you could run a custom firmware loader (like Pasta) and then install unsigned *.CIA (cracked Nintendo DLC games) with FBI software.
You need to be on system firmware 9.2.0 or lower for the "real" magic (aka install unsigned *.CIA) to take place however.
With my updated 9.9.0 2DS I can launch homebrew in user mode with Tubehax, I can't however load CFW Pasta (no Kernel mode access) this also prevents me from installing *.CIA.