Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Show Import Dialog
PREF_IMEXPORT_SHOW_IMPORT_DLGParameter: Show Export Dialog
PREF_IMEXPORT_SHOW_EXPORT_DLGParameter: Merge on Drag & Drop
PREF_IMEXPORT_MERGE_ON_DDParameter: PREF_IMEXPORT_MERGE_ON_DD_INFO
PREF_IMEXPORT_MERGE_ON_DD_INFO