Just to be sure I understand the request. You're wanting to be able to set, on all of your users, the tags within the "app" tag group, is that correct?
If so, I would usually recommend doing that through the app code instead. So, when the user performs some action, the SDK can handle automatically adding those "default" tags to that user.
If that's not possible, that's definitely okay. You can add those tags via the method you mentioned, that is, using the API to set the "default" tags for each user.