Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Maximum Angle
MDATA_BEVEL_ANGLEParameter: Extrusion
MDATA_BEVEL_OFFSET1Parameter: Extrusion Variance
MDATA_BEVEL_VARIANCE1Parameter: Inner Offset
MDATA_BEVEL_OFFSET2Parameter: Inner Variance
MDATA_BEVEL_VARIANCE2Parameter: Subdivision
MDATA_BEVEL_SUBDIVISIONParameter: Create N-gons
MDATA_BEVEL_CREATENGONSParameter: Type
MDATA_BEVEL_MODEParameter: Path
MDATA_BEVEL_PATHParameter: Preserve Groups
MDATA_BEVEL_PRESERVEGROUPS