Hello.
I ran into a problem when, having applied a metal grate texture to the mesh, I now need to impose another metal texture on the sides, as if a cutoff place. A texture has been added to the base model, but what should I do with a cut of the displaced metell grate texture, how to add a texture there?

You need to apply UV coordinates inside the slice_out /obj network as well. Then make sure to choose a texture for that material.

As you're using polyextrude, you can take advantage of output groups to create a side primgroup. You can use it to define another primgroup for the remaining geometry.

In Solaris, "Scene Import" and "SOP Import" LOPs have this "Subnet Groups" parameter which enables division of the imported data into geometry subsets based on its primitive groups. Geometry subsets can be used for material assignment downstream.

Here's an example file.