Hopefully someone can offer you a better explanation, as I'm not sure what tools you'd need to use, etc. But, I'm 100% sure it's doable.
You could probably find all the info by searching around the forum.
huh? NTR doesn't need to work with gateway. What the person is saying, if you have a New 3DS and you installed the NTR 2.x on it, then you can boot into the NTR and put the gateway save onto the cartridge. I do not know how, I just understand what the person said.