Okay, I MAY have stumbled upon a solution to this, and quite by accident, and I can't get it to work everywhere. Working on VIII Landgraab (empty apartment next door to the Fengs), I noticed this happening when I used the room tool to redraw a room so I could wallpaper the room inside with Shift+Click. I noticed the wall texture outside disappear, but when I hovered over it with literally any wallpaper, it would restore the default outside texture to the building, and only to the outer segment of the wall I had just drawn (IIRC). This was in the bathroom with the red sink, the master bedroom, where the outside wall is not completely covered with windows. It still worked on the master closet, even though its only outer wall is covered in windows and the drywall glitch was only visible with cutaway/walls down. It still charged me money for the wallpaper, so if you are attempting this in an apartment with Sims living in them you should probably pick a cheap wallpaper so it doesn't cost them a lot, as it will not apply anything other than a predetermined pattern outside.
However, I could not get this to work in 1020 Alto Apts (Diego Lobo's place), where the walls are completely covered in windows, and the drywall is only visible with cutaway/walls down and I do not have access to a whole wall panel/square on the exterior to hover the wallpaper select over.
So while not a complete solution, it is something worth trying. I do not know what apartments other than these two that this trick might work on, but I thought I would reply in case this might give someone on the dev team or a modder an idea of where to start looking to maybe fix it.
