I was just looking to change the value of the ${PRODUCT_NAME} variable and found this:

1. Go to “Targets” and then do a “Get Info” on the application name.

2. In the window that pops up, go to the “Build” tab.

3. In the “Setting” column, go to the “Packaging” section and expand it if it isn’t already expanded.

4. In that section, change the “Product Name” entry to the desired name.

Found here: http://discussions.apple.com/thread.jspa?threadID=1643724