Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Outer Radius
PRIM_TUBE_ORADParameter: Inner Radius
PRIM_TUBE_IRADParameter: Rotation Segments
PRIM_TUBE_SEGParameter: Cap Segments
PRIM_TUBE_CSUBParameter: Height
PRIM_TUBE_HEIGHTParameter: Height Segments
PRIM_TUBE_HSUBParameter: Fillet
PRIM_TUBE_FILLETParameter: Fillet Segments
PRIM_TUBE_FSUBParameter: Fillet Radius
PRIM_TUBE_FILLET_RADIUSParameter: Switch to Updated Tube
PRIM_TUBE_SWITCH_TO_UPDATED