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.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10