A new experimental feature was introduced in Moodle 3.6 for context freezing. When enabled this removes all write capability for all users (including admin).
However, you cannot apply this at the site level. Technically you may be able to in the backend, but you cannot in the UI.
In terms of your query for 3.5, you can do the same thing as you suggest, but you ned to do it for all write permissions, not read permissions.
Note: This will have some weird consequencs - students will not be able to view their assignment submissions for example. This is the reason that the feature is experimental.
Andrew
However, you cannot apply this at the site level. Technically you may be able to in the backend, but you cannot in the UI.
In terms of your query for 3.5, you can do the same thing as you suggest, but you ned to do it for all write permissions, not read permissions.
Note: This will have some weird consequencs - students will not be able to view their assignment submissions for example. This is the reason that the feature is experimental.
Andrew