Enrich a serialized proto message without affect the existing property?

I have a chain of 3 services (A => B => C) and a simple proto message (M). The message:

message M {
   string name = 2;
   int32 id = 2; // new key
}

A and C hold the latest version of M (above) while B holds an old version (without the id key). B receives an instance of M, enriches it with name value, and passes it to C.

Is there a way to preserve the values of the 'id' while B modifies this message, so C will have both 'id' value and the enrichments?

Thanks!