A method and system to help prevent legacy devices that do not support a service feature such as uplink-downlink subcarrier shifting from connecting with an access node on a carrier where the service feature should be applied. An example method involves use of Network Signaling (NS) values that are used for spectral emission control. Per the disclosure, the access node could broadcast an NS value that legacy device are not configured to understand but that newer devices are configured to understand as relating to both spectral emission limitation and also the service feature at issue. Responsive to the broadcast of that NS value, the legacy devices will therefore not connect with the access node, while the newer devices may connect with the access node and apply the service feature.