I am wondering how you can configure Discourse to give all anonymized users a common username such as “deleted user” or “anonymized user”, instead of having unique anonymized usernames.
AI-generated summary
The discussion revolves around configuring Discourse to assign a common username, such as “deleted user”, to anonymized users instead of unique usernames. thea initiated the discussion, and Don suggested manually changing the username. Simon_Manning proposed merging anonymized users into a single “deleted_user” account, emphasizing the importance of anonymizing the user first to avoid email address conflicts. thea inquired about managing this process via API, and Simon_Manning indicated that while anonymizing users has API documentation, merging users does not, and suggested exploring existing topics or reverse-engineering the Discourse API.
As admin you can change their username manually. Just go to their profile and edit the username. 
But I believe it should be unique as well so maybe just rewrite the anon to deleted_user and keep the numbers.
Users can be merged so you can change the username of one anonymized user to deleted_user as @Don suggests, then merge all other anonymized users into deleted_user.
When you want to do this in future, anonymize the user first and then merge into deleted_user. It’s important to anonymize the user first because the account being merged into will take on the email address as its secondary email address.
I see - think that could be managed via API?
I expect the answer is yes but I only see API documentation for anonymizing users, not merging them, so I will go with probably. For merging there may be existing topics about it or there is this: