With Ingame Username Change Mod 1.7.10 you can change your ingame username. Obviously does not work in online mode servers only if you reset to your original user name. It will work only for singleplayer.
Screenshots:
Mod Showcases:
How to install Ingame Username Change Mod 1.7.10
Download Links for Ingame Username Change Mod 1.7.10
For Minecraft 1.7.10
For Minecraft 1.8