As I know for now there is no official option in geant4 to implement your own cross-section. That is possible like this https://geant4-forum.web.cern.ch/t/custom-cross-section-for-hadronic-processes/3860/5 if you don’t care about pruducs of reaction, or like this https://geant4-forum.web.cern.ch/t/custom-cross-section-for-hadronic-processes/3860/4 if you need to take into account products.