Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Texture
PRIM_RELIEF_TEXTUREParameter: Size
PRIM_RELIEF_LENParameter: Width Segments
PRIM_RELIEF_SUBWParameter: Depth Segments
PRIM_RELIEF_SUBHParameter: Bottom Level
PRIM_RELIEF_BLEVELParameter: Top Level
PRIM_RELIEF_TLEVELParameter: Spherical
PRIM_RELIEF_SPHERICALParameter: Switch to Updated Relief
PRIM_RELIEF_SWITCH_TO_UPDATED