GBA health disclaimers are an odd one. A few people looked at it and a generic removal is probably off the cards, however it boiled down to a fairly simple method. Alas the only game I cared for with it was a puzzle game and the Japanese version lacked it so I have not really investigated it.
Most of the time with cart based consoles it is not a loading mask either so you can do more. There are GBA binary patching cheats but most AR/GS stuff for the GBA is memory focused ( http://doc.kodewerx.org/hacking_gba.html
) and it will probably be a binary edit rather than a memory edit to pull this one off.
The general theory is pretty simple -- the game will likely execute a branch when you press start/press the any button on the title screen. You want to find this branch and insert it earlier in the code, it will probably not work as the first thing you do as the console will probably want to set some registers and initialise IO and whatnot, any point after that (which will probably still be under a 10th of a second from boot) should be good though. If you are more used to PC debugging or debugging for earlier consoles (the NES and to a slightly lesser extent the SNES has some nice branch logging/compare/isolation features) then the GBA does not do quite as well here (no$gba developer version and vba-sdl-h are fine tools though for most other GBA debugging/hacking purposes though) but you should still be able to get it done.
With all that said if you are going an emulator then it might be just as easy to use a savestate -- done right you will probably come in before the SRAM/EEPROM/Flash is read and then just load straight in after that.