How can I edit a Master Material to display 'Grass Material Functions' in an Instance?

I have a Master Automatic Landscape Material which contains 2 Grass Functions. (See Image Attached)
The functions are used in conjunction with the landscape material so if for example I have a desert map I can assign a cactus mesh (in Grass01) to the sand material and a bush mesh (in Grass02) to my dirt material…
(So far, so good)

But if I want to use this material on different types of terrain I have to keep duplicating the Master Material rather than create instances, as there is no way to access the Grass Function slots from within the Instance. (If I could, I could just relink to other Grass Functions and change the mesh).
Currently, once the 2 Grass Functions slots are used up, I cant go and create another type of terrain (e.g. a jungle map with palm trees and ferns) without duplicating the Master Material and the original Grass Function folders.

In summary: What can I do to display the Grass Function slots within the Instance?

Any help greatly appreciated!