Is this about the cross section? If yes, from the PROPOSAL side, this can be disabled by removing this line from the code (or not adding the created object to the following vector)
I think the proper way to handle this in the long run is to make it configurable. In air FLUKA provides the more complete model as it includes nuclear effects but since we have the implementation for PROPOSAL we might as well keep it. It would allow us to quantify the nuclear effects by comparing the two. The two solutions proposed above are workarounds as they switch off (by hard coding) hadronic interactions in FLUKA or in PROPOSAL.