Are you referring to the x-axis labels (the labels "12/31/2014", "1/31/2015" ....)?
You can set the labels to any text you like. The exact method depends on how the chart is set up.
In the simplest case, if your code provides the x-axis labels as a StringArray, you can simply modify your StringArray based on user input, and then redraw the chart. For example, consider the sample code below:
The x-axis labels are set up using Axis.setLabels. You can provide a user interface to allow the user to edit the list of labels, then set up the StringArray based on the user input, then redraw the chart. Usually, no additional code is needed to redraw the chart, as it is the same code that draws the chart in the first place.
If some chart setup, your code does not provide and cannot predict what are the x-axis labels (eg. the labels are automatically determined by ChartDirector based on the data). In this case, other method would be needed. Please let me know if this is the case.
Re: How to set the axis label between tick marks for the Line chart
Sorry for my mis-understanding. If the labels are configured using Axis.setLabels, you can
put the axis labels in between the ticks by using an "indented axis" and shifting the shifting the ticks by 0.5 unit.