One question: why? What good reason can one have for playing NES games on a GBA in 2018? There are so many better handhelds for such purposes, not least because the GBA actually has a lower resolution than the NES, meaning the Classics released had modified graphics to make them look better.
Not only that, but there are several actual NES emulators for the GBA, which would give far better functionality than injecting a ROM, plus be a lot less effort.
I have a Wikipad tablet which comes with a gamepad attachment, so playing NES games on a huge HD screen is way better than trying to hack a GBA. Seriously, I can't think of a single good reason to do this.