At this time it is not possible to move the "primary" designation from the starting BU to a new, update BU in use in an account.
As a team grows and changes, this option to move the Primary from one Business Unit to another is needed. While we can reassign Projects and more between BUs, we cannot change the designation of "Primary" which can cause many issues over time.
Example:
Optum is currently going through an internal revamp and has several BUs. The GPS BU is the "Primary" BU and has been. At this time, they want to move their entire library and metadata to an unused , empty BU so they can work behdin the scenes to revamp and clean content fully. They then were hoping to reassign the "Primary" to this new BU for a more seamless transition for their team.
With the current setup, we cannot offer this as an option. They cannot work behind the scenes to completely redo their CCL adn transition users over, after the fact. Now they will have to potentially pay PS for two content migrations (1 to the empty BU and then again when it moves back to GPS BU when complete).