Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Mode
HAIR_MIRROR_MODE
Parameter: Auto Root
HAIR_MIRROR_ROOT
Parameter: Strength
HAIR_MIRROR_STRENGTH
Parameter: Search
HAIR_MIRROR_SEARCH
Parameter: Guides
HAIR_MIRROR_NEIGHBORS
Parameter: Coords
HAIR_MIRROR_COORDS
Parameter: Mirror
HAIR_MIRROR_PLANE
Parameter: Object
HAIR_MIRROR_LINK