How to change the sorting order of dates in the drop down property of spotfire
You can apply custom sorting to STRING columns. 
One way to achieve your goal is to create calculated columns for the Year and Month, and use these in your date axis. Then you can apply a custom sorting in Column Properties > Sort Order on your data table.
In Spotfire text area, for drop down property, by default sort order for date column is coming with the oldest to latest. We need to display the dates order from newest to oldest. Can you please advise. 
Default Order:12/29/2015 12/30/2015  12/31/2015    01/01/2016
Needed 1/1/2016   12/31/2015  12/30/2015  12/29/2015
Thanks