Pokemon Brilliant Diamond - Downgraded Game Version, Save File Causes Black Screen/is Corrupted

[johtto]

Hello,

I have an interesting problem: I recently installed Pokemon Brilliant Diamond on my modded switch and have been playing for some time. I eventually wanted to patch the game from v 1.1.0 to v1.3.0, so I did and the game was working fine. Now, I want to mod the game but needed to downgrade from v1.3.0 to something older such as v1.1.3. When I re-installed the older base version and cleared the update requirement in DBI, the game simply does not load. The nintendo switch splash screen appears, then nothing but a black screen.

I posted in another forum here: https://gbatemp.net/threads/switch-noob-paradise-ask-questions-here.488277/post-9844602, where another user suggested deleting the save file. Deleting the save fixes the black screen issue, but I lose my progress. Using PKHeX, I was able to open the save backup just fine. I tried adjusting the "SaveRevision" property from "52" to "44" which changes the "SaveRevisionString" property from "1.3.0" to "1.1.0". After restoring this modified save, the game no longer boots to a black screen but, after the title screen the game complains that the save data is corrupted and must be deleted.

I need suggestions for how to "downgrade" the game version for a save file so I can go back to an older version of the game.

Edited June 5, 2022 by johtto

[Atrius97]

The format of the savefile is different between game versions. Changing one value doesn't magically fix the size or format of your savefile.
If you do not have an older backup of your savefile from 1.1.0 or earlier, you're probably just out of luck.
If you want to develop a tool that trims off the extra data and converts the savefile back to an earlier game version, or try to do it by hand, you're in mostly uncharted territory.

Edited June 5, 2022 by Atrius97

[johtto]

19 hours ago, Atrius97 said:

The format of the savefile is different between game versions. Changing one value doesn't magically fix the size or format of your savefile.
If you do not have an older backup of your savefile from 1.1.0 or earlier, you're probably just out of luck.
If you want to develop a tool that trims off the extra data and converts the savefile back to an earlier game version, or try to do it by hand, you're in mostly uncharted territory.

Thanks Atrius; I wasn't expecting it to be easy, but I also don't expect it to be that difficult either. Since saves are like a database, data can be new and old data can be removed from one revision to the next, as long as I know what the differences are I can somewhat reliably determine what needs to be rolled back. Beyond doing a bit by bit comparison of the file formats myself, I was hoping someone out there would have hit this too and could point me in the right direction