This functionality is not available of the box, but I have a suggestion for you.
You can create a user control that changes the title and the page keywords. Now that you have the Tag id in the query string, what you need to do in your user controls is to:
1. Take the ID of the tag, and use the ContentManager to find the actual tag
2. Change the page keywords and title during the controls Page_Load event.
I hope this helps.
the Telerik team