Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Show Objects
ID_CA_XREF_SHOWOBJECTSParameter: Loaded
ID_CA_XREF_LOADEDParameter: Generator
ID_CA_XREF_GENERATORParameter: Reference
ID_CA_XREF_FILEParameter: ...
ID_CA_XREF_FILE_SELECTParameter: Proxy Ref
ID_CA_XREF_PROXY_FILEParameter: ...
ID_CA_XREF_PROXY_FILE_SELECTParameter: Namespace
ID_CA_XREF_NAMESPACEParameter: Animation
ID_CA_XREF_ANIMATEParameter: Frame
ID_CA_XREF_TIMEParameter: Offset
ID_CA_XREF_OFFSETParameter: Scale
ID_CA_XREF_SCALEParameter: Position
ID_CA_XREF_PIVOT_POSParameter: Scale
ID_CA_XREF_PIVOT_SCLParameter: Rotation
ID_CA_XREF_PIVOT_ROTParameter: Swap
ID_CA_XREF_SWAPParameter: Reload
ID_CA_XREF_REFRESHParameter: Open for Edit
ID_CA_XREF_EDITParameter: Options...
ID_CA_XREF_OPTIONS