Yes, with the new Custom option for the User parameter you can implement your own User parsing behavior. Your custom code should return a single user id, single user object, array of user ids, or array of user objects. In your case you'd need to write the code to check all the way up the reply chain and output an array of user ids to execute the action on, which should just be a CB Activity action.
Sending a notification when someone directly replies to your comment or comments on your activity however is significantly easier. There's a system action for activity comment notifications already using "CB Activity - Comment Notification". There isn't one for comment replies yet and have added a feature ticket to implement one.
forge.joomlapolis.com/issues/6963
It is highly unlikely specifically what you're wanting would be implemented. That'd be an extremely heavy operation. For example what if a comment has 500 replies? That's 500+ notifications on every new reply.