Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Clear
MGSELECTIONTAG_CLEAR
Parameter: Invert
MGSELECTIONTAG_INVERT
Parameter: Display Indices
MGSELECTIONTAG_NUMBERS
Parameter: Use Fields
MGSELECTIONTAG_USEFIELDS
Parameter: Tolerance
MGSELECTIONTAG_FIELDTOLERANCE
Parameter: Use Deformed Points
MGSELECTIONTAG_FIELDDEFORM
Parameter: Fields
MGSELECTIONTAG_FIELDS