Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Clear
MGWEIGHTTAG_CLEAR
Parameter: Invert
MGWEIGHTTAG_INVERT
Parameter: Use Fields
MGWEIGHTTAG_USEFIELDS
Parameter: Use Deformed Points
MGWEIGHTTAG_FIELDDEFORM
Parameter: Fields
MGWEIGHTTAG_FIELDS