Clutz presents a really valid way to go, but I'm gonna give another take.
If you're fairly new to training, you might consider sticking with your ME exercises for a while, cycling the weights up and down like a powerlifter (5/3/1 would be an example). As a beginner, you need to get reps in with your big exercises so that you can get comfortable with your form. WS4SB is only giving you one session a week with a given exercise so just when you're starting to get in your groove you'd be changing exercises. Not always a huge change, but still a change.
Both approaches work, it's just a matter of which one fits your goals better.
Accessory work is a different matter. I'd feel free to change it up every few weeks until you find some exercises that really work for you and then you can milk them for a while.