After you select all of the duplicate rows, then all you have to do is to find the rows you don't want to be selected and then unselect them.
Here is an example
Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/big class.jmp" );
dt << select duplicate rows( Match( :sex, :height ) );
// Find the rows that should not be selected
theRows = dt << get rows where( :weight == 92 );
// Unselect those rows
For( i = 1, i <= N Rows( theRows ), i++,
Row State( theRows[i] ) = Selected State( 0 )
);
Jim