Mobile: Can notifications be edited after it has been sent?

It depends on the type of notification.

If the notification has been sent to the device, it cannot be edited; it's technically gone.

If the notification is triggered based on behavior (when you enter / exist the Audience), then the workaround would be: duplicate notification > edit > delete original immediately. This will allow new users to receive the updated notification, but the notification cannot be edited for users who have already received it.