It should work as long as you use a Calculated value and uncheck "Do not replace existing value of field (if any)". By doing that, updating referenced fields down the line will prompt the field to re-calculate. If this doesn't work, give more information so I know why it's not working.
Hi Brian, thanks for the tip, although i do have a question about this. Would old data be replaced, as the database has 13 years of data already in it?
Sorry for the delay, holidays. Depending on the shema of the current database and how you change it, the data will remain intact. Without an actual copy of the database, though, I'm reticent to give you a "do it this way" answer. The best thing to do would take a backup of your database and test. DO NOT make schema changes to your live database without knowing exactly what happens.