Highcharts set x-axis categories

You can do this with the setCategories method found on the Axis object. See the reference documentation for axis here: http://www.highcharts.com/ref/#axis-object

Example: http://jsfiddle.net/4tuvC/

Since Highcharts 5.0.0 you can use the update() function to update the chart options after render time:

Data.chart.xAxis[0].update({categories: xAxisCategories});