Several years into the era of "BattleTag", Blizzard has finally implemented a system to pay for a new BattleTag name. As players often change their "main" characters, the demand for being able to change your BattleTag has grown over the years.
All Battle.net account holders get one free change to their BattleTag, and after that, additional changes will cost 10$ USD. The name can be anything within Blizzard's naming guidelines, and the name doesn't have to be "unique". Like before, the numerical ID after the name is selected by Blizzard and acts as a unique identifier. You cannot select these numbers.
All friends on your current Battle.net Friends List will remain on your list, they will not be affected by this change. Your name will immediately update across your Battle.net client and mobile devices.