Possible to edit the "backup" save in Gen 3?

[Keitaro2]

As I understand it, there are two saves stored in a gen 3 save--the main one and a backup of the previous save. I accidentally saved my game after doing something I didn't mean to, and am wondering if it is at all possible to access the backup save and get a Pokemon back from there. I couldn't find any information in the editor about this, so forgive me if it isn't possible or if I'm misunderstanding how this works.

[Kaphotics]

Challenge yourself to learn how hex editors work and the layout of the save file -- set the byte width to 0x1000, then you can corrupt the most recent save blocks so the game loads your backup instead.

Save data structure (Generation III) - Bulbapedia, the community-driven Pokémon encyclopedia

PKHeX does not allow loading of the backup portion, only the most recent part of the save.

I guess you could debug the program to tell it to load the not-latest portion, but that isn't something worth explaining in detail.