wat
Just open the gbxmodel and create a new material for every shader. The only thing you need to make sure of is the same name. Attach the entire model together to 1 object, then use the region select or whatever its called in editable mesh to select certain parts. Apply the appropriate material to it by looking through sapien at the same time to see where what goes. Its really not that hard

. By the way, this can be a much easier process by unslecting the import materials button when importing, then doing what I said.
The only thing it might not import is #sun, I've had countless origional Halo skys do that, so I suggest making your own when doing so, and making your own sun.lens_flare tag.
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