How to lock users during a system freeze?

Summary

Due to a system cutover we need to freeze the TBE system, so users cannot work in it.

Content

Due to a system cutover we want to freeze the TBE system. What we want to accomplish is that users cannot do anything in the system for a specific period of time. Only two users should be able to do configuration changes in the system during the freeze. Putting users on 'no access' role during the freeze and them put them back to their original role is not an option as at user level also lots of configuration is done on user list views and application views.