Hi @neilwebbcbs!
There are different ways of managing permissions in AEM. You may want to refer to my reply in this thread [1] for additional details around that. As already mentioned by @arunpatidar, the Netcentric AC Tool [2] is a good way to manage groups and their according ACLs through code which will ensure a consistent state across different environments and instances.
In addition to that, it would be interesting to learn why you need to change the permissions of the OOTB anonymous user. From my experience, it's usually recommended to not tamper with the OOTB users or groups, especially when it comes to the ones that are integral part of certain system functionalities, such as the admin or anonymous user. For most cases the better option is to create a custom project-specific group and base that on the OOTB ones. As always, there are exceptions to this and some requirements might actually need changes to the anonymous user. But this has to be a qualified and justified decision. The documentation on the OOTB users and groups [3] mentions that the anonymous user should not be deleted or disabled to avoid unexpected behavior. Similarly, changing their permissions might have unexpected and/or unwanted effects. So in any case please make sure to thoroughly test any permission changes that are performed for the OOTB users and groups on lower environments and take a backup before applying the changes.
Hope that helps!
[1] https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/restrict-user-to-publish-the-page-from-author-instance/m-p/589715#M147204
[2] https://github.com/Netcentric/accesscontroltool
[3] https://experienceleague.adobe.com/docs/experience-manager-65/administering/security/security.html#built-in-users-and-groups
