BootNTR can do that too though.That's good news for me,i still use cheat codes with some games.
http://gbatemp.net/threads/bootntr-11-1-nfirm-support.441566/
Usage is as simple as loading cheats into a "plugin" folder on the SD card, and installing BootNTR.
Once you run BootNTR from the home menu, run the game you want to cheat in, and press X+Y to open a realtime menu. From there you can use your cheats plugin.
You'll know it has worked if the Nintendo 3DS logo screen flashes green whilst the game is booting.
Gateway cheatcodes can be converted to NTR cheat plugins as well.
http://gbatemp.net/threads/release-gateshark2ntr.436504/
For that matter, Gateway's own A9LH installation method is actually far worse than the Plailect guide, it breaks DS game support.Please read the posts above. Just because you can, doesn't mean you should or it's officially supported.
The official Gateway a9lh.bin file doesn't work with the Plailect guide setup either, unless you use a workaround.
https://gbatemp.net/threads/tutorial-using-luma3ds-with-gateway-on-v2-a9lh.431691/
Really you should just be moving away from using Gateway completely, and just opt for a nice big memory card in your 3DS to kept all your games installed in a single place.