You can make a custom material and if you use specific custom parameters name then UE will fill your material instance properly with the data coming from the FBX.
e.g.: DiffuseColor, DiffuseColorMap, DiffuseColorMapWeight. You can have a look at /InterchangeAssets/Materials/PhongSurfaceMaterial OR /InterchangeAssets/Materials/LambertSurfaceMaterial for example of parameter values you can use.
I can make a custom material like this, and then I import the FBX with “MaterialInstance” and using this Material as my master material. UE will attached the texture as it would have done with default material
for your Interchange Blueprint Pipeline, use the Interchange Editor Blueprint pipeline. this is available since 5.5. Load Asset is editor only function.
a) I did not manage to do that yet. Asking for some pointers.
In theory, at the Execute pipeline level you should be able to add your own Interchange Material Factory Node to the Base node container. Then you could set up the different properties yourself and Interchange would create the new material for you.
b) At the Execute Post Import you could do some content browser operation. But Execute Post Import function is called per asset created so maybe not the best place for what you need to do.
I used a special pipeline that gives more insights on translated nodes that comes from reading the file, and factory nodes that are created and modified by default and custom pipelines.
The preview button only give you partial information on factory nodes
You can use this view for debugging by adding the DefaultGraphInspectorPipeline at the end of your pipeline stack. This window will popup by itself.
Scene or Level import with Interchange is not fully tested yet in 5.5 so it is disabled by default. If you want to use your custom pipeline with level import then you should enable Interchange for FBX Level import.
Use the following CVar