How to restrict users from logging in temporarily?

Hi All - We will be performing a major implementation in production in a few weeks and we will be performing a lot of UI changes, approval rule changes, etc.

We do not want any user to perform any kind of transaction during this window. We want to see if there is a way to mark the environment as being under maintenance or under outage while a selective few users can still access the environment for performing these changes?

I know there are few other ways to achieve this such as removing security roles temporarily from users during this window and reassigning them back at the end of the implementation, but would like to understand if the outage option is possible.