Can you be a little more clear on what you mean by “change the browser tab”? Can you point to the page you are having a problem with and describe the problem you are trying to solve?
For example are you trying to rename a page to change the name of a menu option?
Sure. When I am on the cart page, the browser tab says Mysite|Cart and not Goat & Shepherd Mohair|Cart.
OK - this is clear now! I have reported this as a possible bug. If I find a work around I'll update this post.