Mikko Virenius

This WordPress Plugin allows an admin user to add comments even if the comment thread is closed.
Features
<ul>
<li>No options panel</li>
<li>No extra configuration required</li>
</ul>

Admin Can Always Comment

I use this on CSS-Tricks for the obvious reasons. I close comments after a certain amount of time, but as an admin, I want to be able to leave comments whenever I want to. 

Works Great with 4.9.6

This plugin allows an admin user to add comments even if the comment thread is closed.

room34

NEW IN VERSION 2.0.0: Users with a custom role will now only see the posts or pages they are assigned to. We’ve also streamlined the admin interface for easier configuration, and included additional instructions to help you get the proper capabilities assigned to your custom roles.
Custom Access Roles allows you to create, edit and delete custom roles for editing content. It was created to fill a need for a role editor plugin that is focused on providing easy-to-use admin tools for restricting content editing access. It is not concerned with restricting viewing access on the front end.
It is specifically intended for large sites with multiple content editors, where editors (by role, not individually) need to be restricted to only being able to edit specific areas of the site.
With this plugin, administrators of large sites have relatively fine-grained control over which user roles can edit which content, making it possible to manage a team of editors without concern that they will (accidentally or deliberately) edit content they should not have access to.
You can define a fully customized set of capabilities for each role, along with defining a specific set of post categories, pages, and custom post types to which those capabilities apply. For all other content, the role will have read-only access.
Custom Access Roles provides an easy interface for managing these roles and capabilities, with checkboxes for each capability grouped by the standard roles they’re associated with, plus checkboxes for each post category, page, and custom post type, presented in an organized hierarchy.

Custom Access Roles

Create custom roles with editing capability for only specific pages, categories and post types.

Admin Can Always Comment vs Custom Access Roles