keycloak: add a user from a deployed authenticator without using the keycloak admin client

Question

I have a custom authenticator which should create a user in case they don't exist. The following snippet creates a user:

@Override
    public void authenticate(AuthenticationFlowContext context) {
        String someUserId = ...;
.....
        AuthenticatorConfigModel config = context.getAuthenticatorConfig();
        KeycloakSession keycloakSession = context.getSession();
        UserProvider userProvider = keycloakSession.userStorageManager();
        RealmModel realmModel = context.getRealm();
        UserModel user = userProvider.addUser(realmModel, someUserId); <-- this creates the user
        }

I can also create the UserRepresentation in the following way:

        UserRepresentation rep = new UserRepresentation();
        rep.setUsername(...);
        rep.setFirstName(...);
        rep.setLastName(...);
        rep.setAttributes(Collections.singletonMap("someAttribute", Collections.singletonList(...)));
        rep.setEnabled(true);

Is there a way to update the user representation without using the keycloak admin client with its REST API Calls? Of course, I can use it but I thought there could be an easier way if I am deploying the code to the keycloak deployments themselves.