Found the answer. Boy that is certainly an annoying unproductive way to change the default.
Essentially, the only way to change the value is at the point of inserting the variable.
Instructions here: http://forums.adobe.com/thread/847978
If it's any consolation...we all feel your pain and have raised this issue with Adobe several times. Feel free to put in an enhancement request using the link on this forum site so that you add your voice to those of us wanting this 'feature' changed.