On the assignment Area object there is a User field that we can use to assign the owner of a record. We are finding that in our territories we need to assign more than one user to different fields. A manager field, a partner user field... ect. I can create a new user lookup field and then in our Process Builder automation I can trigger an update to the field. The problem is that the users cannot update the new custom field on the Assignment Plan because it does not show up on the Assignment Plan edit page.

if you modified the vfpage to display fields in a field set then we could add/remove fields to the set and it would show up without any additional coding.