Once the user clicks submit, check if the user being renamed has more than 50k edits, and then add another checkbox asking that they're totally sure they want to do the rename to remind them about the edit count limit that requires sysadmin supervision.
|Resolved||Glaisher||T116238 On Special:GlobalRenameUser, check if the username has more than 50k edits, and ask a "are you sure" question|
|Resolved||Steinsplitter||T187547 Change notice (allowHighEditcount) limit to 100k for global rename user|
I'd recommend setting the threshold much lower, or simply dropping the threshold altogether and always asking for confirmation. My edit count is substantially more modest, but it is mine, and those edits are my identity as an editor.
I forgot to mention it in the task, this is about making it easier for global renamers to know when they're going to hit the 50k limit that requires a sysadmin to supervise the rename for potential issues (policy), not about whether they should actually make the rename - there's already an additional confirmation step for that.