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