You have the following primary data source that contains a dimension named Dorm_Code.

Using relationships: You can use relationships to link the secondary data source with the primary data source based on a common field. This will allow you to use fields from both data sources in your visualization without creating new fields or duplicating data. You can then replace references to update the dimension values. For example, you can use relationships to link the updated dorm codes with the primary data source and then replace Dorm_Code with Dorm_Code_New in your visualization.

https://community.tableau.com/s/question/0D54T00000C5ldZSAR/update-data-view-based-on-dimension

To update existing visualizations with new codes without changing the field name, using relationships to bring in the secondary data source is appropriate. Then using Replace References allows you to update the references from the old dorm codes to the new ones while maintaining the existing field name.