Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Maximum Angle
MDATA_BEVEL_ANGLE
Parameter: Extrusion
MDATA_BEVEL_OFFSET1
Parameter: Extrusion Variance
MDATA_BEVEL_VARIANCE1
Parameter: Inner Offset
MDATA_BEVEL_OFFSET2
Parameter: Inner Variance
MDATA_BEVEL_VARIANCE2
Parameter: Subdivision
MDATA_BEVEL_SUBDIVISION
Parameter: Create N-gons
MDATA_BEVEL_CREATENGONS
Parameter: Type
MDATA_BEVEL_MODE
Parameter: Path
MDATA_BEVEL_PATH
Parameter: Preserve Groups
MDATA_BEVEL_PRESERVEGROUPS