That's not the reason for adding the "this" word, it's just to make it easier to understand that "Star" is a verb and not something else.You'd then have to change "Mark this Conversation as Unread" and "Leave this Conversation"
I mentioned it in another thread. That row of controls is exclusively for THIS conversation. So there should not be a need to clarify that it's for THIS conversation.
Other actions usually use the Call to Action type buttons at the end of the breadcrumb container.