I'm not sure if this would work but you may try to restrict the "write" permissions via /crx/de 'Access Control' tab
Remove the "jcr:write" and "rep:write" permissions on the path where your CFs are stored for "original" node for specific user/group.
E.g. say you've a Cf at '/content/dam/<we-retail>/<some_path>/myfragment' then you'd add a new entry for a user/group (based on your requirements)
rep:glob as /content/dam/<we-retail>/<some_path>/myfragment/jcr:content/renditions/original where you'd add all relevant permissions except the write permissions. You may add a REGEX for the same based on your requirements. This way you'd not have the write permissions on the original (master) version of CF but all other nodes including variations.
reference - https://jackrabbit.apache.org/oak/docs/security/authorization/restriction.html