First of all, some notices:
I will not be responsible for any mischief you do on your behalf. Make a backup copy of Explorer.exe if you are not sure about it. All the files are to be taken from where you have installed your windows. Like "C:\Windows".
And the after effects will be: like this one.
So, legally, I am all safe now.... LOL going to deepest
First of all, you'll need a software named Resource Hacker which is available over here.
Next, start it up, and open the "explorer.exe" file. Navigate to String Table\37\1033 inside it.
If you have classic version enabled, go to 38
Next step is to edit the value of field inside 578 to whatever you want, like I did it to "hjpotter92".
Now, save the file. You can use "save as..." to save it with another name, like I edited it to "explorerhjp.exe".
Hacking the registry....eh something complex here. Go to registry editor by clicking on "Start\run..." type regedit and then navigate to "HKEY_LOCAL_MACHINE\ SOFTWARE\ Microsoft\ Windows NT\ CurrentVersion\ Winlogon". Search for a string named shell and edit its value to "explorerhjp.exe".