See this is why the n64 mod community is awesome! They keep it alive. My ONLY compliant is... Duh duh duh. Why aren't we seeing Glover, and geomon? Those obsurce n64 characters. That's pretty much it tbh.
In settings there an option that says "player tags" from there you can make several name tags. After that in the CSS, when you choose your character, select the smash icon next to the character model which will bring up a menu. From there you can change player tag to whatever name you want