They won't, and they will notice it. ICS is not out on the Bionic, and ICS is drastically different from GB. You MAY have luck doing the transaction over the phone, but what will probably happen is once the phone goes to where ever it goes (it's going to go here regardless if you do it in store or over the phone). If they see you've rommed or leaked they will end up billing you in full for the replacement phone.
Again, you may luck out, but you're taking a huge risk either way. Any way around this would be considered fraud, and cannot be discussed on this forum.
The only thing I can think of is to wait for the OTA to come out, go to it, and then request replacement. Ultimately, your scenario is one of the reasons it was highly recommended to not go past 232. If you ran into problems with your phone you couldn't fxz back to 905, and get a replacement effortlessly.
Sorry bud, but it looks like you're just gonna have to wait this one out.