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