Based on your screenshots, changing the name isn't enough. You should also remove the Rank, coins, Activity, Merit, Avatar, personal text and Trust score. And the usernames shouldn't be shown in quotes. But if someone quotes a user, the forum database should still store the correct quote for others to avoid turning it into plagiarism.
You forgot signature though lol, with signature identifying the user is made a little bit easier by just checking the spreadsheet (at least there’s an accurate number of suspected members)..
this opens the possibility of editing a quote with no backref to the original.
easy to abuse.
IMO if there’s an anonymous post then all comment/post below it should be anonymous so maybe having a board that does that aka “Anonymous board” could solve that but if possible having all post within the thread to be anonymous (everything should be freely expressed .
However there’s still an issue, the user is logged in to make the anonymous post which means the mods can still get the particular user if the UID is linked to the anonymous post, so on a second thought posting through an Alt is still the most suitable option to posting anonymously..