In the latest update, 1.7.8, Minecraft has been prepared to support name changes. This is exiting news to those who vigorously regret their choice in username, especially me, who has the name: jpm739.
For more information provided by Mojang below.
We have pushed out an update that supports name changes, however we will not allow name changes until a future date. For information on how name changes will work, please see these frequently asked questions.