So, after all these years, we still have no mod or easy way to change the main menu background back to how it was before the expansions? Isn't it weird?

I am trying to make a mod to change the wooden texture and size of the box that pops up when the player engages anyone in conversation. I have spent hours digging through the game folder and exploring the assets but I can't seem to find the files or the data related to what I want to do. Any leads?

No clue, I'm sorry. I have zero knowledge of mods, you may have a better chance to get your questions answered at the Nexus Mod Community.