Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Top Radius
FIELD_CAPSULE_TOP
Parameter: Bottom Radius
FIELD_CAPSULE_BOTTOM
Parameter: Height
FIELD_CAPSULE_HEIGHT
Parameter: Direction
FIELD_CAPSULE_DIRECTION
Parameter: Clip to Shape
FIELD_CAPSULE_CLIP