I've used that tutorial several times - reread it a bit more carefully, as he explains both the easy and the hard way. You just have to pay attention a bit more to which way is which.
You basically need to open your own library, but enter a command line (a bit tricky and annoying) that copies over a part from another library, and then finally edit it for your own evil plans.
Not if only Eagle was intuitive . . . that would be amazing!