Hi Katie,
There isn't a native feature to specifically add a manual entry column to the Manage Users page. You can use Groups like Matt suggested to help you manage users via the groups interface. another option is to create an Employee table in Quick Base that specifically lines up each user with the region they belong to. It could have a full list of each user using a user field and then important information like region can be added in to serve as a more fleshed out resource to go with your Manage Users page. A number of apps use this when building out custom permissions based upon Regions, etc. They are also used in HR apps to help track other details about the Employees like specific responsibilities, pay, etc.
If you feel that being able to add a manual entry field to Manage Users would be a beneficial feature in Quick Base, I would encourage you to submit feedback regarding this via our Feedback Platform - UserVoice - Which can most easily be accessed from the My Apps page in Quick Base by clicking on the orange Feedback tab or at
http://quickbase.uservoice.com . This forum is used by our development team to explore customer suggestions for enhancements / changes to the platform. Many of the items that have been suggested by customers have already been incorporated into Quick Base and I would encourage you to participate as well.
