How To Add The Same Shader/Material To Multiple Objects? I want to apply or use the same material for multiple objects. How can I do this without doing it per object ? The target objects already have their own materials and I don't want to override them. I just want to add new material slot  and same material across multiple objects.
I can't use Ctrl+L to link material because it will replace existing material.
Any solution ?

The real case is, I'm building a house (3 floors) with basic furnitures. So I got many walls, floors, windows, doors, kitchen set , fence etc.
All these objects has their own basic material setup :

wall : concrete, white paint
door : wood panel, inox, black frame
window : glass, inox ,black frame, alluminium
etc.

There is a unique wall (wall A) has a material i want to copy.

wall A : concrete, white paint, SECTION

So I want to use this section material into all other objects on the scene (those other walls, doors, windows, kitchen set etc). There are many objects so I'm looking a way to apply this section material without manually applying per object. And I want to keep the existing material :

wall : concrete, white paint, SECTION
door : wood panel, inox, black frame, SECTION
window : glass, inox ,black frame, aluminum, SECTION

I can't find a way to apply selected material to multiple objects without replacing the existing material.
Thanks
import bpy


# Input material's name to append
matname = &quot;SECTION&quot; 

if matname in bpy.data.materials :
    mat = bpy.data.materials[matname]
    objs= bpy.context.selected_objects
    for obj in objs :
        if obj.type == &quot;MESH&quot; :
            if matname not in obj.data.materials :
                obj.data.materials.append(mat)
else :
    print(&quot;Material '&quot; + matname+ &quot;' does not exist&quot;)