You will need to open the object and edit the 3D script.
Search for all of the lines that say ....
material "Plastic - White"
There are more than I show in the image.
This is hard coding the material to Plastic - White.
Replace the line with ...
material MainBoxMaterial
This will now use the material parameter that you want - make sure you don't use quotes.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11