[data to object]

You can make a selection of the objects a create a group.  The selection can be done manually by clicking on the 3D View .  Perhaps by spelling of name if that happens to be your case.

    import bpy
    
    for x in bpy.data.groups["MatGroup"].objects:
        print(x.name)
        o = bpy.data.objects[x.name]
        o.material_slots[0].link = 'OBJECT'

    

The above script is still being tested. It is a starting point after you have created a group with the name in quotes.  Consider use only on a **discardable copy** of your file.  Standard disclaimer.  Backup your files every hour and use Scripts at your own risk.  I will try to complete a Script if I have time.

You may need to change your search to ... Python Script to [data to object] material.  You may also look at Material addons in the User Preferences.  Please improve my search suggestion.

A Python Script might include statements 
which can be seen in the information (info) window


A Python script can perform [data to object] for you by iterating through that group and making the change.
Currently I am not including a Script.
If someone does not provide a Script in the near future and time is of the essence, for the above you may choose to do it manually.

Multiple Materials to One Material

I saw something I believe here at BSE an question which brought up a material matching in the form of a Script.  I believe it reduces multiple matching materials into one material.
That script may be on the [Related column] on this same BSE page, 

copy linked materials nodes to local nodes.

[![enter image description here][1]][1]

Above image shows some material addons.  I have not researched these.  The documentation button seems to link to non existant files.


  [1]: https://i.sstatic.net/4GKJk.png