“Febuilder’s gaiden magic patch is very old. I do not recommend using it.”
You can say that again. My hack is becoming semi notorious for the amount of bugs it causes people!
If I implemented it using buildfiles, can I then go back to working with Fire Emblem GBA Editor or is it one or the other?
No, sorry.
A custom build is basically a buildfile except it’s febuilder friendly and takes 5 minutes to load onto a rom instead of 5 seconds to build your rom. I recommend experimenting with the beginner’s buildfile to start.