The good news is that 2012 pays more attention to the family default value for the individual families you place than the override. This means you can change the value for the individual family you are placing now and then if you switch to something else, when you return to place more of the families (or another type) you'll get the default value assigned to the family instead of the "rogue" change you made to one earlier.
Daniel Stine (author of several Revit books) created this video and passed it along to me (no audio) to share when he wrote to ask me if I noticed the change. I did and was grateful for the change. Since he went to the trouble to make a video, seems a shame not to share it!