In this moment, beside direct editing, one cannot change realm name
within a war.
But one can change what the realm name refers to in admin as you have
mentioned.
With this, one can even change the authentication mechanism after
deployment as follows:
1. the war refers to realm "myrealm"
2. create a "myrealm" in admin
3. deploy the app
4. change the definition of "myrealm"
Shing Wai Chan