at an owner client of a stateful switch over infrastructure, where the owner client owns a particular owned field that is included in a message sent between first and second endpoints, where the first endpoint is a sending user client of the stateful switch over infrastructure that is sending a message of a particular message type and a particular version number and where the message includes a foreign-owned field which is the owned field owned by the owner client and the second endpoint is a receiving user client of the stateful switch over infrastructure:

registering with the stateful switch over infrastructure the size of the particular owned field included in all versions of messages of the particular message type and the offset of the owned field in the message;

at the sending and receiving user clients of the stateful switch over infrastructure:

registering with the stateful switch over infrastructure the message of the particular message type containing the particular foreign-owned field;

registering with the infrastructure user client transformation functions for the user client, where the user client transformation functions transform between different versions of a particular message type;

reserving a placeholder in the message of the particular message type for the foreign-owned field, with the placeholder having a size determined by the information registered by the owner client;

at the stateful switch over infrastructure:

copying the foreign-owned field from an input message of a user client;

invoking transformation functions registered by the user clients to transform the message of the particular type between different versions:

invoking transformation functions of the owner client to transform the foreign-owned field between versions to create a transformed foreign-owned field;

copying the transformed foreign-owned field into the placeholder of the message after the message has been transformed.