ShrineFox.com Forum

Alright, this might seem like a minor thing, but I'd like to try modifying the message box in P4G to be the plainer/darker style that was in OG PS2 P4.

But I can't for the life of me find the textures, even with this as a guide. It's possible they're not TMX files in any of the PAC packages, but that doesn't elucidate where it'd be otherwise.

Sorry to disappoint, but afaik the message boxes in P4G are hardcoded so there is no file (TMX or otherwise) that contains information on how they look, it's determined directly in the game's code (the exe).
The only way you could change them would be through a Reloaded mod that hooks into the code that renders them. While it's theoretically possible it'd be a lot of very hard work (CBT) so yeah, unless you want to go through that you won't be able to change them.

Damn, that was beginning to become my suspicion. I couldn't even find it in the PS2 assets to use as reference for its location. (Since the file structure appears to be 99% the same.) Sadly, patching the code directly might be a bit beyond my knowledge at this stage.