You don't have to change your healthy extras at all - they're yours, and you can use them for whatever you wish. Although it can help you to mix things up a bit if you find yourself maybe hitting a plateu.
As PWP said, it stops you from becoming bored and straying from the plan. I also think it's good to give your body a variety, it keeps it "on it's toes", if you like, as I often find when it's used to the same things, that's when you're weight loss can slow down a little.
I do Red / Green days rather than Extra Easy, so I too get the double Healthy Extra's each day. I always have two B's and they are varied each day - HiFi bars, cereal, WW wholemeal pitta, etc. I usually stick to 1 A choice which is normally either milk, grated low low cheese, low low cheese spread, mozzarella, or philly light. There's that much choice out there, there is no reason why you should have to have the same thing every single day - unless of course you want to!