Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Radius
PRIM_CAPSULE_RADIUS
Parameter: Height
PRIM_CAPSULE_HEIGHT
Parameter: Height Segments
PRIM_CAPSULE_HSUB
Parameter: Cap Segments
PRIM_CAPSULE_FSUB
Parameter: Rotation Segments
PRIM_CAPSULE_SEG
Parameter: Switch to Updated Capsule
PRIM_CAPSULE_SWITCH_TO_UPDATED