How would I re-program a GBA cartridge?

[WizardCM]

NOTE: This is not so I can pirate games. I simply want to extend my understanding of how the Gameboy Advance cartriges work.

Firstly, I'd like to know what's in a GBA (Gameboy Advance) cartridge and if it's possible to "re-program" it. By that I mean remove the existing game and replace it with another (or with a program).

My idea is to open a cartridge up and replace the existing read-only flash memory with (maybe?) parts from a USB Thumb drive. I'm guessing this would also need some sort of software similar to the R4 (for the DS), but not in that pirate-ish way. Maybe this would also mean the ability to run custom applications on it like a word processor or similar.

Also, if I did want to put a single game on it (possibly an existing GBA ROM?), for testing purposes, how would I go about doing it?

Thanks for any help in advance. :)

[The Teej]

Technically feasible with a lot of soldering and reprogramming, but to be honest if you want to program for the GBA you're better off getting a flash cart and running unsigned code off of there. It's WAY easier and probably a lot cheaper too.

[Solid Knight]

Or you could get a flash cart since they are designed for you to do this very thing.

[+InsaneNutter MVC]

You can use a device such as the Gameboy Transferer 2 to read / write to GB/GBC and GBA cartridges (providing there writable, unless you have a flash card there not)

If you were to some how modify a retail cart and make it writable I dont see why you wouldn't be able to write to it with the Gameboy Transferer 2.

I did a little write up on how to backup saves with the Transferer 2, maybe the software will be of some use to you? As for modifying a retail cart thats beyond me, good luck though it sounds like an interesting project.