# https://blender.stackexchange.com/questions/68143/all-textures-upside-down

import bpy
import bmesh

def mission1(mesh):
    bm = bmesh.new()
    bm.from_mesh(mesh)

    for uvt in mesh.uv_textures:
        uv_layer = bm.loops.layers.uv[uvt.name]

        for face in bm.faces:
            for loop in face.loops:
                loop[uv_layer].uv[1] = 1-loop[uv_layer].uv[1]
    bm.to_mesh(mesh)
    
    mesh.update()

if bpy.context.mode != 'OBJECT':
    bpy.ops.object.mode_set(mode='OBJECT')

meshes = set()
for obj in bpy.context.scene.objects:
    if obj.select:
        meshes.add(obj.data)

for mesh in meshes:
    mission1(mesh)