Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Enable
HAIR_RENDER_TAG_ENABLEParameter: Auto Time
HAIR_RENDER_TAG_AUTOTIMEParameter: Start
HAIR_RENDER_TAG_STARTParameter: Stop
HAIR_RENDER_TAG_STOPParameter: Mode
HAIR_RENDER_TAG_MODEParameter: As Fill Hairs
HAIR_RENDER_TAG_HAIRSParameter: Length
HAIR_RENDER_TAG_LENGTHParameter: Scale
HAIR_RENDER_TAG_SCALEParameter: Count
HAIR_RENDER_TAG_COUNTParameter: Segments
HAIR_RENDER_TAG_SEGMENTSParameter: Restrict
HAIR_RENDER_TAG_RESTRICTParameter: Limit
HAIR_RENDER_TAG_TRAIL_LIMITParameter: Trail
HAIR_RENDER_TAG_TRAILParameter: On Death
HAIR_RENDER_TAG_DEATH