Actually I think this is redundant; since the EC2 instance private IP address is wired into the registration resource, this should absolutely happen if the EC2 instance is replaced during a CloudFormation deployment. It will not happen if the EC2 instance is replaced outside of a CloudFormation/CDK deployment but that's ok; that should happen only in extreme circumstances when AWS irrecoverably loses the customer instance, which is beyond the scope of this basic stack.
Actually I think this is redundant; since the EC2 instance private IP address is wired into the registration resource, this should absolutely happen if the EC2 instance is replaced during a CloudFormation deployment. It will not happen if the EC2 instance is replaced outside of a CloudFormation/CDK deployment but that's ok; that should happen only in extreme circumstances when AWS irrecoverably loses the customer instance, which is beyond the scope of this basic stack.