Amxx's default ban system work on either on SteamID or IP, they don't ban nicks.
Next, you can't evade a ban if you constantly change your nick, you can either be banned using your userid (status, first number) and using amx_ban #userid or the admin can just use amxmodmenu and ban you using the menu, the menu bans using userid too so there's no escape changing the name.
Still, I may have understood wrong, does this thing you want have anything to do with amxx plugin scripting ?