Good for you!
There is a BIG difference between knowing some commands...and having a well trained dog. A well trained dog will be willing to follow commands when there are all sorts of other distractions around. A well trained dog will listen the first and only time you give a command.
Start with baby steps....he's been doing things this way for 4 years...so it will take time and training.
I would also suggest you enroll in a CGN class....they have them so that people and their dogs can get prepared for the test. Many local dog clubs run them...or even back to a basic obedience class.
The trainer would be able to teach you how to teach him to except a stranger greeting him.
Glad I got your wheels in motions!
and I'm sure your female Rottie will be happy to be bugged less.
Gina