The Modify->"Merge Material(UV)" option is great and works really well for a lot of things. I use it to merge all of my cloth material together before export. I'm not an expert but the results have been much better than all my attempts to do something similar with external software.
The problem is that the UV unwrap results are unpredictable. To see this you can run the merge, close your project without saving, open it up again and merge with the exact same settings you will get a different UV layout than you did the first time. Since the results are different every time it means that you can't use it for baking multiple versions of the same materials.
In my case, I have a suit made up of different parts. Each part of the suit has its set of textures (diffuse, normal, etc). I merge the material on the entire suit and export it to Unreal Engine 5. It works great and saves on storage and memory requirements.
But I have a collection of different colored suits. Each suit has its own set of diffuse textures but otherwise uses the identical textures to the other versions of the suit. I can merge each version of the suit and export it to UE5 but this is where it becomes a problem.
These merged materials aren't interchangeable because each version of the suit has different UVs and the materials were baked differently from each other. Ideally I would only need one version of the suit and one set of textures, plus a set of merged diffuse textures.
So I'm asking if there's a way to get consistent results from the material merge. If not, can I request this as a feature?