Disable everything except reading (2.4.8-2)

Hi, We are going to move everything from a 2.4.8-2 installation on one server to a 3.x installation on a different server.

During this process, which might take a few days, we would like readers to be able to view articles on the old server, but we want to disable everything else.

We figured out how to disable new user registrations and submission of new articles. We can also rely on editors to not make changes until they are told it is ok. But how do we prevent reviewers from submitting reviews?

Thanks, Brendan.