It returns user now.

routes/api/users/index.js

@@ -62,8 +62,8 @@ router.post('/:user_id/status', authorization.needed('ADMIN'), (req, res, next)
 
 router.post('/:user_id/displayname', authorization.needed(), (req, res, next) => {
   UsersService.setDisplayName(req.params.user_id, req.body.displayName)
-    .then(() => {
-      res.status(204).end();
+    .then((user) => {
+      res.status(201).json(user);
     })
     .catch(next);
 });

services/users.js

@@ -365,7 +365,10 @@ module.exports = class UsersService {
       .then((displayName) => { // displayName is valid
         return UserModel.update(
           {id},
-          {$set: {'displayName': displayName}});
+          {$set: {'displayName': displayName}})
+        .then(() => {
+          return UserModel.findOne({'id': id});
+        });
       });
   }