I am new to Yii so I have not had to do this yet, but I always thought that I could make the change to my DB and then use Gii to preview the newly generated version and view it in in my browser and see how it in would change my module without overtiring my code.
So I tried it to see, maybe Gii was preventing this because the file already existed. I was right you can preview updated code in Gii of existing models but what was really smart was that it provides a link to a diff showing the difference between my current model and what a newly generated one would be.
The more I use Yii the more impressed I am, that is very cool.