Change Rougness Multiple Materials at once

Development Asset Creation
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4

Probably the only way would be to export the materials to the gl Transmission format .gltf

Modify them all with a custom tool that would change roughness parameter via regex and save the file.

Or you could also export out all materials and try replacing all text strings in the files
"roughnessFactor": 0.5
with
"roughnessFactor": 1.0
for instance with a text editor like notepad++

Once all of the files were edited you would have to reimport them into unreal

example part of a file with parameter roughnessFactor:

"materials": [
		{
			"name": "Mat3",
			"pbrMetallicRoughness":
			{
				"baseColorFactor": [ 0.974336147, 1, 0, 1 ],
				"metallicFactor": 0,
				"roughnessFactor": 0.5
			}
		}

The only down side to this method is that once you import a gltf file it will add a material expression to translate it back to a normal material. Perhaps there are other importers for unreal that clean this up.