Blender script to clear all Custom Split Normal Data from selected objects. Simply select all the objects and run the script. This is useful when importing a bunch of objects used in game development, such as the output generated from https://github.com/Dylancyclone/VMF2OBJ/

clearCustomSplitNormalsData.py

import bpy

selection = bpy.context.selected_objects

for o in selection:
    try:
        bpy.context.view_layer.objects.active = o
        bpy.ops.mesh.customdata_custom_splitnormals_clear()
    except:
        print("Object has no custom split normals: " + o.name + ", skipping")