Steps to Reproduce: # create a domain
/subsystem=security/security-domain=mydomain:add()
{
    "outcome" => "success",
    "response-headers" => {"process-state" => "reload-required"}
}

# add JSSE settings:
/subsystem=security/security-domain=mydomain/jsse=classic:add(keystore=[{"url" => "${jboss.server.config.dir}/jboss.keystore","password" => "secret"}])
{
    "outcome" => "success",
    "response-headers" => {
        "operation-requires-reload" => true,
        "process-state" => "reload-required"
    }
}

# double check
/subsystem=security/security-domain=mydomain:read-resource(recursive=true)
{
    "outcome" => "success",
    "result" => {
        "acl" => undefined,
        "audit" => undefined,
        "authentication" => undefined,
        "authorization" => undefined,
        "cache-type" => undefined,
        "identity-trust" => undefined,
        "mapping" => undefined,
        "jsse" => {"classic" => {
            "additional-properties" => undefined,
            "cipher-suites" => undefined,
            "client-alias" => undefined,
            "client-auth" => undefined,
            "key-manager" => undefined,
            "keystore" => [{
                "url" => "${jboss.server.config.dir}/jboss.keystore",
                "password" => "secret"
            }],
            "protocols" => undefined,
            "server-alias" => undefined,
            "service-auth-token" => undefined,
            "trust-manager" => undefined,
            "truststore" => undefined
        }}
    },
    "response-headers" => {"process-state" => "reload-required"}
}

Now quit and stop the server, then look at the xml:

      <security-domain name="mydomain">
         <jsse/>
      </security-domain>

So the settings are not written to the xml configuration file
Workaround: Workaround Exists
Workaround Description: edit the xml manually
project_key: JBPAPP6

Adding JSSE setting to a security domain works in-memory, but they are not written to the xml file.