An expression comparing min and max years for % change would be possible but simpler if rows were added for those years without any orders (see attached).
The idea of using the ColumnNo() to change the expression in the total of a pivot table would also be handy - as shown in this thread http://community.qlik.com/thread/11316. by Daniel Rozental.
If your Change % represents a kind of fact, like Revenue Change %, that you'd want to see if you only selected a single year, you could get the script to work out the change by using Peek() in the load, maybe to a summary table (see second attached for the basic idea).
A cumulative script using Peek() is shown here http://community.qlik.com/thread/31436 by swuehl.