Trainers, translations and other ROM hacks to be applied on GameBoy Advance ROM images.
Tools, file formats and techniques for editing commercial games are also discussed in GBAtemp's ROM hacking section which will have additional information for the GBA, DS and more.
Many tools are useful across systems (a hex editor works much the same regardless of the system you are working on) so do also check out the Filetrip's general programming tools section.
I haven't played my Switch n a month or so, just been playing Xbox, and just picked to play lil and Damn that A and B, X and Y being reversed always gets me.
@BigOnYa:
I haven't played my Switch n a month or so, just been playing Xbox, and just picked to play lil...