Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Reduce Children Combined
POLYREDUXOBJECT_REDUCE_ALL_AS_ONE
Parameter: Reduction Strength
POLYREDUXOBJECT_STRENGTH
Parameter: Triangle Count
POLYREDUXOBJECT_TRIANGLE_COUNT
Parameter: Vertex Count
POLYREDUXOBJECT_VERTEX_COUNT
Parameter: Remaining Edges
POLYREDUXOBJECT_REMAINING_EDGES_COUNT
Parameter: Preserve 3D Boundaries
POLYREDUXOBJECT_PRESERVE_3D_BOUNDARY
Parameter: Preserve UV Boundaries
POLYREDUXOBJECT_PRESERVE_UV_BOUNDARY
Parameter: Boundary Reduction Angle
POLYREDUXOBJECT_REDUCE_BOUNDARY_ANGLE