I would like to dig this back up as I have a similar request. I need a newly registered user’s username to be changed to Firstname_Lastname automatically, but I am already using an SSO (Memberful) and they refuse to do this for ‘security concerns’ 
so I have to do it manually each time a person signs up and inevitably the user emails me about it before I have a chance to change it because it is super boring using only the first name. So is there anyway to to add this as a task? It would of course have to check if the name exists and add a numeral behind it if so. Thanks!