Cannot change nickname while quieted on channel and cannot register to be un-quieted because not using a registered nickname Catch 22

/nick mlncn
mlncn #snowdrift Cannot change nickname while banned/quieted on channel
/msg NickServ IDENTIFY MySecretPassword
mlncn80 is not a registered nickname.

Couldn’t find it documented anywhere, least of all Freenode’s registration documentation, but the workaround is very simple: Supply your username to the nickserv identify command (it goes before the password).

/msg NickServ IDENTIFY mlncn MySecretPassword
You are now identified for mlncn.
/nick mlncn
You're now known as mlncn