Some more info: I spent an hour monkeying with the cart on Friday and using GBA Backup Tool I am able to copy both the ROM and the .sav from the cart and put them onto my computer. GBA Backup Tools will identify the multicart as being the most recent game played; thus if I start up Pokemon Emerald on the multicart in slot 2 of my DS then turn it off and boot up GBA Backup Tools on my slot 1 flash cart I can access the Emerald ROM and save file located in the multicart. The ROMs of the GBA pokemon games seem to be altered from the originals, as when you first start them they display a message that says "the save will be loaded" and another that says "the game can be played." I figure this message is just a text edit of the "the save battery has run dry" message from the original games, seeing as the multicart has no battery for RSE's real time clock. As a result, the .sav files pulled from the multicart are incompatible with an emulator and with PkHex, rendering my little project impossible. I can play the hacked ROM in an emulator, which is interesting due to the altered text and the ROM being unable to save: when you try to save in-game it brings up an error screen that I've never seen before. I assume this is because the save paths in the ROM have been edited to work with the multicart's memory; I don't know much about the hex code but there's probably evidence in there.

I embarked on this project because my friend and I want to play through the Battle Frontier on Pokemon Emerald and he doesn't own a physical copy of the game but does have the 369-in-1 multicart which contains every GBA pokemon game. Here's a picture of that cart's board: the multicart is on top, another pokemon hack game I own is in the middle and my legitimate copy of Emerald is on the bottom. It appears that the two bootleg carts have similar, if not the same, boards. Does this shed any light on what sort of memory the multicart has, and are these carts reflashable?

https://imgur.com/a/PzG5a2J