Hi Henrique,
Indeed, when you initially sign up for the developer edition, there is no choice of availability zone - we tried to limit the choices to a minimum...
But now that you got authorizations for our AMI, you can launch new instances directly from AWS Console without having to got through the license agreement process again (still bound to the same license of course). In AWS Console, go to the AMI view and then set the filter to "Private AMIs". You should see the HANA Developer Edition Rev 48 AMI and you can launch an instance from there. On the first step, you can choose the availability zone. Use the Security Group that was created earlier and your existing key pair. Last thing to do after the creation is that you assign your existing Elastic IP Address to the new instance - these settings are specific to a region, but independent from AZ.
hth
--juergen