[MDL ED] Changing the material of an entity

[SuspecM]

So I was playing around in the model editor and found out that you can change or add a "submesh" for an entity (picture here https://imgur.com/a/YRjkxQx)
The only problem is that while it shows the chosen material on the model in the modeleditor, it resets to the default material of the model in-game and in the model test menu. Is there a way to change a model's material this way or is it just a waste or time?