I recall covering something like this before.
I do not think any known GBA games use bank swapping (it is popular on older systems for multicarts though), there are some oddities as those doing master codes might have found (Phantasy Star collection being the big one, more http://doc.kodewerx.org/hacking_gba.html#nonstandard
) and I must confess that I have not paid any real attention to the ? in 1 bundle games. Some flash carts and I suppose technically some homebrew would use bank swapping/page select and reset though.
Anyway as henke37 said it is more likely to just be a function, and probably not one that works standalone so you would probably want to call it after the initial IO and everything-- in case you were unaware the basic technique for GBA binary finding is the very first byte of the ROM is the first instruction and it is almost invariably a jump to the end of the header. At the end of the header there will usually be some IO, setting up stack pointers and whatever else and then a jump to somewhere in the 08?????? region which marks the actual binary.
Scene type intros hitched themselves to various places but subverting that jump in the 08?????? region is a good one to go for.
Finding out what the option menu does is fairly standard menu hacking, however rather than the usual trying to launch with options, forcing a given language, going right to a given mode or finding hidden debug menus then you need to go a bit deeper. Same principle though and it will likely still be some jump you can hopefully replicate earlier in the ROM.