Step by step:
- Double-click the Material Instance you want to modify to open it in the Material Instance Editor.
- Click the Hierarchy button in the Toolbar, then choose SketchUpMaster > Open In Editor from the contextual menu. You’ll see the graph for the master material open up in the Material Editor.
- From the main menu, select File > Save As, and save the master Material to a new Asset in your Project.
- Go back to your Material Instance, and find the General > Parent setting in the **Details **panel. Set this reference to point to your new master Material.
Now, when you modify the graph for your master Material, those changes will affect the instance.
Hope that helps.