Try this:
From the assemble room.
In the scene window -> instances tab. Click on the object in the list.
See if there is a 'shading' tab in the top right window.

If there is:
You can see the 'shading domains' (which should be the same as your material assignments) applied to the object.
Then double click on a 'shading domain and you can edit the domain's shader directly from there.

If that isn't available/doesn't work; I don't what else to tell you.

Friends don't let friends use booleans.