and why would you want to do that?
so you can troll and quit in games and then change name and do it all over again without ppl knowing it?
go into steam profile and change it there then
steam-settings-friends-profile name
Let me guess, you have Windows 8? The steam profile name works in windows 7, but for some reason in Windows 8 it seems to use your windows user account name or something. Not having windows 8 I don't know how to change this (only know about it because a friend of mine encountered it and he couldnt be bothered to figure it out since he only plays lan with me)
You will only use your Windows username while in LAN games. Internet games will continue to use your steam name. Unfortunately, there isn't a way to change that at this time.
Might this explain the issue? (from the 2K forums)