Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Migrate
CAP_MIGRATE_BUTTON
Parameter: Start Cap
CAP_START
Parameter: Start Cap Steps
CAP_STARTSTEPS
Parameter: Start Cap Radius
CAP_STARTRADIUS
Parameter: End Cap
CAP_END
Parameter: End Cap Steps
CAP_ENDSTEPS
Parameter: End Cap Radius
CAP_ENDRADIUS
Parameter: Fillet Type
CAP_ROUNDING
Parameter: Phong Angle
CAP_PHONG
Parameter: Hull Inwards
CAP_HULLINWARD
Parameter: Hole Inwards
CAP_HOLEINWARD
Parameter: Constrain
CAP_CONSTRAIN
Parameter: Create Single Object
CAP_CONNECT
Parameter: Rounding UVW Keep Shape
CAP_UVWROUDING
Parameter: Type
CAP_TYPE
Parameter: Regular Grid
CAP_REGULAR
Parameter: Width
CAP_REGULARWIDTH