Hello guys,
I successfully changed my account name, full name and directory without losing any data, app & system settings (maybe only the Safari view setting but all my bookmarks were there as I left them, I don't use iTunes but it will probably be ok). It's almost 4 am where I live so I will not include any screenshots or anything like that but try to explain how I did it as simple as possible, you know.. for you guys
FYI: I tried the top suggestion and it worked indeed but I lost my data, setting etc. Basically it created a new empty user folder. I didn't loose the original one but since there was no account pointing to it, it was inaccessible.
Like always backup your system with Time Machine. You won't be needing the backup but just in case you know.
Step 1: Create a temporary admin account.
Step 2: Log in the new admin account.
Step 3: Open the User & Groups tab under System Preferences and change the account name, full name and directory of the desired account (no spaces ).
Step 4: Open the Terminal and gain admin access by typing "sudo su" and than entering your password. Navigate to the users directory (type "cd /Users") and rename your original account directory like you did in Step 3. These 2 name MUST be identical.
Here it gets a bit tricky but you will be alright.
You have to do one more change in the Terminal. I actually did it after I logged back into my normal account, after I renamed it and it still worked. Maybe you can do it while being in the temporary admin account. I don't know, you can try but here is what you have to do.
Step 5: Again - Terminal with "sudo su" access: locate this file in your system "/Users/YOURUSERNAME/Library/Preferences/MobileMeAccounts.plist" and rename it ("mv OLDNAME NEWNAME"), don't delete it at first. "YOURUSERNAME" here should be the new one. After that just restart and log back as you would normally do and everything should be there.
NOTICE: if you log into your normal account before doing Step 5 it may look a bit different but don't scare. Just run the step in the terminal and restart. Afterwards the system will generate a new file and you can delete the old one.
BTW if you wonder where did I found about that file, it's here: http://apple.stackexchange.com/a/151623 <- YOU SHOULD READ THIS ARTICLE!!!
Anyway I hope my words will help you. Sorry if I made any spelling/grammar mistakes.
Cheers!
Tedobear