look, why dont u put a ~n on nick, so there is no reason to this

and no need a on nick event here, cause u mute their ip's... so if ppl change the nick, the mute will be there

ON *:NICK:{ 
  if ($nick == %Mute.Nick) {
    set %Mute.Nick $newnick 
  } 
}

like
mode +b ~q: $+ $address(%Mute.nick,2)
mode +b ~n: $+ $address(%Mute.nick,2)

so this, ppl will not evade the mute if mute is given on nick

by the way, you need to unset Global vars

unset %mute*