Yes, this can be done with security assist.
you will need to add a new column to the users table for EmailVerified, set the default value to 0, then set up an admin page that review the registrations and update the email verified to 1.
you'll also need to edit the login to store the email verified value in a session variable, and set up an acccess rule to only allow access if the email Verified session is equal to 1.
this is very similar to a Double Opt in system, where an email is sent on registration, and the user needs to click a link to verify, accept the site admin is doing the verification.
We have a tutorial for double opt in on the data bridge support page:
that should give some of the specifics needed, you'll just need to modify it slightly to create the pages for the admin to change the verified value.