Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Draw
BELT_DRAWParameter: Set
BELT_SETParameter: Clear
BELT_CLEARParameter: Show
BELT_SHOWParameter: Belt on:
BELT_LINKParameter: Influence
BELT_FParameter: Influence Map
BELT_F_MAPParameter: Hover
BELT_SParameter: Hover Map
BELT_S_MAP