Customized values for built-in fields are stored in the project1. That ensures that everyone using the project sees and uses the same set of customized values without importing or exporting field values.
You have the ability to customize default values and value choices for the built-in fields such as "Use Case Status" or "Assigned To." For example, you may want to enter the names of your project team members as value choices for the Assigned To field. From the Tools tab of the ribbon bar, select Built-in Fields:
Once you have created a set of custom fields or have customized your built-in fields, you can export them to a file for import into a different use case project or to share with other team members.
And, if you have a set of customized built-in fields that you'd like to use for brand new projects, you can click the "Save as defaults for new projects" check box at the bottom of the Built-in Fields form before clicking "OK."
1Versions 2012 and later
If there was a Save as defaults for new projects checkbox in the Custom Fields form, then wouldn't that save the users time and effort of exporting/importing custom fields between all projects?
Good point Theresa!
Also, it would be useful to remove some of the built in fields. For example, my organisation prefers to use MoSCoW for prioritisation so we end up with the generic 1-5 priority field, and another MoSCoW field. Also, implementation status has little relevance to us and takes up space on the screen.