The genesis isn't a prime, it can't switch back. The prime can switch to genesis and back though.
Hmm, interesting remark
I've reread Josh's post, and this is what he says (and that's where I got the info from Ian, not the feature list or comparisons):
"Oh! And Hashlet Primes are going to be able to switch to SHA-256 at the end of next week. You will be able to switch it between Scypt and SHA on the fly! We will explain how this will work next week"
Based on that, Prime's can switch back and forth. Okay...
But a Hashlet Genesis is a Prime. My Zen Dashbaord shows the Genesis listed under "Prime Hashlets". I can make a screenshot but no time now, and likely you can see for yourself anyway:)
So, I'm keeping the door open that the Genesis can switch back and forth also. If not then the only "Prime" to buy is a Hashlet Prime and not a Genesis.