Link external_ids directly to device token for ionic push rather than via ionic auth

Hi I looking to use Ionic Push Notification and send notifications to specific users/devices or specific group of devices. For this purpose, I have to inject some external_id while registering the device for push notification and using that id, I can send notification to that devices. Currently token can be linked to user_id from ionic auth service and I don’t see an option to link custom id with token while registering or saving the token. Some thing like below

push.register().then((t: PushToken) => { return push.saveToken(t, {external_ids: ["cust0123974", "restaurant12394"]}); })

Authentication is not required for users of my app and I am not planning to use ionic auth. Is there a way I can send push notifications to specific devices without using ionic auth ?

same question here, what is the best approach to link my custom user_ds (saved in a mysql db) and device tokens?