As I said, there is not much documentation on the ShapeFileReader.
Yes, the simplest and fastest way to do this is to replace code occurrences of GraphHopperOSM with GraphHoppperSHP (I don’t recommend this for production though). You might need to change some parameters etc. I haven’t done this before. Have a look at the ShapeFileReaderTest to see how to correctly instantiate the GraphHopperSHP class.
Also have a look at this issue, that I created after you asked this question. A PR improving this would be very welcome :).