I have submitted a pull request to include the changes I made to add the ability to push notes to all subscribers of a channel, based on the recipient format, and also have the ability to push notes without specifying a recipient, as @64matze tried to do, as the Pushbullet API will default to broadcast them to all the user account’s devices in that case.
// Broadcast to all user's devices
sendPushbulletNote("Title", "Message")
// Send to all subscribers of a channel
sendPushbulletNote("channel-tag", "Title", "Message")
// Send to an email user
sendPushbulletNote("email@example.com", "Title", "Message")