Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Radius
ARRAYOBJECT_RADIUSParameter: Copies
ARRAYOBJECT_COPIESParameter: Amplitude
ARRAYOBJECT_AMPLITUDEParameter: Frequency
ARRAYOBJECT_FREQUENCYParameter: Array Frequency
ARRAYOBJECT_CIRCLEFREQParameter: Render Instance
ARRAYOBJECT_RENDERINSTANCES