There is currently no way to remove or revoke read permissions for a specific charm revision. Read permissions can be removed for everyone but at the charm level, not revision level.
From what I can see in the charm store code this is an API-level limitation:
https://github.com/juju/charmstore/blob/693c346/internal/charmstore/addentity.go#L487-L543 (there’s code for adding charms but not removing).
This functionality would be useful in cases where unwanted information went into the store by accident (such as credentials or some other type of information).
Is there any reason this functionality was not implemented and could this be taken into consideration?