If a file has a nodegraph definition included in the file it is loaded in and is editable.
This can be "dangerous" as the graph implements a definition so it can cause instances to mismatch with the definition.
Here is the reference OpenPBR implementation that has the definition included which folks are using to test this new shading model.
Embedding definitions with instances is also one possible suggested MaterialX mechanism to use custom definitions.
( Note that this renders properly with OpenUSD HDStorm delegate )
Issue
If a file has a nodegraph definition included in the file it is loaded in and is editable. This can be "dangerous" as the graph implements a definition so it can cause instances to mismatch with the definition.
Here is the reference OpenPBR implementation that has the definition included which folks are using to test this new shading model. Embedding definitions with instances is also one possible suggested MaterialX mechanism to use custom definitions. ( Note that this renders properly with OpenUSD HDStorm delegate )
Suggestion
Either hide these nodegraphs (or template them / make them read-only). Here is OpenPBR implementation graph (circled) is shown.