Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Migrate
CAP_MIGRATE_BUTTONParameter: Start Cap
CAP_STARTParameter: Start Cap Steps
CAP_STARTSTEPSParameter: Start Cap Radius
CAP_STARTRADIUSParameter: End Cap
CAP_ENDParameter: End Cap Steps
CAP_ENDSTEPSParameter: End Cap Radius
CAP_ENDRADIUSParameter: Fillet Type
CAP_ROUNDINGParameter: Phong Angle
CAP_PHONGParameter: Hull Inwards
CAP_HULLINWARDParameter: Hole Inwards
CAP_HOLEINWARDParameter: Constrain
CAP_CONSTRAINParameter: Create Single Object
CAP_CONNECTParameter: Rounding UVW Keep Shape
CAP_UVWROUDINGParameter: Type
CAP_TYPEParameter: Regular Grid
CAP_REGULARParameter: Width
CAP_REGULARWIDTH