New Post: LabelFormatString to display other values other than x/y coordinates

Then why you just do something like this:

for(int i=0; i<s2.Points.Count(); i++)
{
s1.Points.Add(new DataPoint(myList1X[i],myListY[i] );
s1.LabelFormatString = (s2.Points[i].X, s2.Points[i].Y)
}

Please note that I haven't tested this (you would probable need ToString() that).
For disabling that you could put a condition before LabelFormatString and redraw the LineSeries whenever the user clicks on that particular CheckBox. Good luck