How can you program a 2nd key or disable the imobilizer on a 2001 focus when you only have one fully programmed key and one programmed for the central locking?

Basically, you cant get there from here. Forget the one programmed central locking keyfob. It has nothing to do with it. Two different systems entirely. The fact that you only have one programmed key is the killer. If you had a second key, then you could program a third yourself. You also cant disable the system yourself. If you want the second key to work, the dealer has to do it using either a WDS, PDS, or NGS scanner.