Changing a Material Instance's Parent Material
You can quickly change the Material that is used as a Material Instances parent by setting a new Parent in the Material Instance editor.
To do this, all you have to do is open the Material Instance and then in the Details Panel under the General section, change the Material that is in the Parent section to a new Material of your choosing.
After doing this, depending on the options of the new Material, the Material Instance Editor will change to reflect the options of that new Parent Material.
Here is a Material Instance that was created using the Material from above as its Parent.
Here is that same Material Instance but this time with the Parent Material changed.
Notice how there are fewer Texture inputs and some new numeric inputs have been added.