In general, techniques are described for modifying control plane messages for subscriber sessions with a network device to add and/or modify discrete information elements and thereby conform the messages to different versions of mobile network specifications, including roaming protocols, executed by different mobile networks or by heterogeneous infrastructure elements within a mobile network. In some examples, an input network interface of a network device receives a roaming protocol message on an interface connecting a first support node of a first mobile network and a second support node of a second mobile network. A roaming protocol module of the network device modifies the roaming protocol message by adding or modifying a discrete information element to conform the roaming protocol message to a roaming protocol of the second mobile network. An output network interface of the network device sends the modified roaming protocol message to the second support node.