Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Strength
MDATA_MGWEIGHTTOOL_STRENGTHParameter: Mode
MDATA_MGWEIGHTTOOL_MODEParameter: Apply All
MDATA_MGWEIGHTTOOL_APPLYALLParameter: Apply Selected
MDATA_MGWEIGHTTOOL_APPLYSELECTEDParameter: Radius
MDATA_MGWEIGHTTOOL_RADIUSParameter: Step
MDATA_MGWEIGHTTOOL_STEPParameter: Pressure
MDATA_MGWEIGHTTOOL_PRESSUREParameter: Show Weights
MDATA_MGWEIGHTTOOL_DISPLAYParameter: Visible Only
MDATA_MGWEIGHTTOOL_VISIBLE_ONLY