Emily:

There is a method to redefine Dimensions, but it is more complex than it should be:
1. Note the name of the Dimension Standard you want to alter.
2. Delete this Standard (the Standard should now read "Custom").
3. Change the dimension options.
4. Click the "Add..." button and enter the exact name of the old Standard.
5. Your Standard should now be changed to the new dimension options in the Views.

The method of redefining a Dimension Standard should be easier and more transparent, like changing a View attribute, unless someone knows of a better method than I have described.

David