As to how to export mesh for handling with separate.py: I didn’t test this, but saving the input file from Prepomax should be sufficient. Safest would be to isolate the *node and *element parts and then include the resulting files into the original input file in place of the original mesh.
In the example collection, the mesh is usually generated by CGX, so it is already available as a separate file and included in the input.
Running the examples with PrePoMax would work via import of the input file once you did the preprocessing using CGX. I didn’t try that though. Perhaps it would be a good idea to store the input files in the github repository even if they are dependent files.