I've been meaning to post this up, but I've been using this set of tools for awhile now to rename accounts and various other tasks. It helps to maintain Google App's using a set of tools that run in python, it's open source and free to use.
To rename an account it's pretty easy, see example.
Changing John Doe to John Smith
in terminal execute the following:
python gam.py update user jdoe username jsmith lastname Smith
Check it out!