Hi Jerry,
Yes - you can assign a data label style per data point:
NBarSeries bar = new NBarSeries();
bar.Values.Add(10);
bar.Values.Add(-10);
NDataLabelStyle dls1 = new NDataLabelStyle();
dls1.ArrowLength = new NLength(10);
bar.DataLabelStyles[0] = dls1;
NDataLabelStyle dls2 = new NDataLabelStyle();
dls2.ArrowLength = new NLength(-10);
bar.DataLabelStyles[1] = dls2;
Hope this helps - let us know if you have any questions.
Best Regards,
Nevron Support Team