There is no means to subscribe or unsubscribe from CBSubs Mailer as it is not a newsletter extension. Users don't subscribe to those emails. They're for subscription status updates. The ACMA policy doesn't apply here as unsubscribe is for commercial emails. You are legally permitted to email them as you please about services rendered. I guess if you're sending emails to advertise/market other plans to them then yes you'd need some unsubscribe functionality, which CBSubs Mailer doesn't provide and recommend using AcyMailing and just subscribing them to a mailing list when they subscribe to a plan.

You could try using CB Auto Actions to do this by setting Triggers to None then using the URL that directly executes the auto action under the Global tab as the URL in the email to unsubscribe. I guess at that point you've a couple of options. You can require them to login for this to work or you can go the route of modifying a user outside of being logged in. To modify them while not logged in you'll need to be user to include their user id in &users of the URL. Then you'd just use a field action as normally to set your field to not notify them. The problem with this is there's no security there. Anyone can set anyone to not receive emails just by knowing their user id. You'd ideally have some sort of security token unique to each user attached to the URL that you'd validate in your auto action.