Inverting material assignment on mesh I am 3D modelling a museum for a game, and I wanted to give every painting a unique texture. On each painting there are 2 different materials: the frame and the painting. I selected each individual painting and assigned it a different painting material, leaving the frame material as the same.
However after changing every single painting material to an individual material, I realized that the parts of the mesh that the painting material and the frame material are assigned on were swapped (each is assigned to the other's). I can't do ctrl + l because all of the individual paintings are going to change. I really do not want to delete them all and then re-add them.
I tried in a duplicate of the project and I couldn't fully delete the 70 materials I made. Is there a way to change the assignment of each painting, while keeping them assigned to their different materials? I also added material utilities, and couldn't find a way, but there might be one.
Some screenshots:
Make sure you're in object mode, then try running this script from the text editor. Save beforehand just in case.
import bpy
for mesh in bpy.data.meshes:
    for poly in mesh.polygons:
        poly.material_index = 1 - poly.material_index