Nice quiz! Got them all except for the one who will be incoming in 2017. Probably tough enough already, but for an additional challenge, you could add the Secretary-General who served in an "Acting" capacity until the first SG was selected: Gladwyn Jebb, of the UK.
Speak to Lie
Breathe (in Gutaires)
Gladwyn the Run (for Gladwyn Jeb, acting predecessor to Lie)
Waldtime
The Great Dag in the Sky (with the iconic wailing vocals set to the word 'Hammarskjöld')
Kofi (to the scansion of Money)
U and Thant (instead of Us and Them - only really works written down...)
Any Cuellár You Like
Ban Damage (featuring the lyric "And if your head explodes with dark forebodings too/ I'll see you on the dark side, Ban Ki-Moon")
Boutros-Ghalipse
Why do so many more people know that Egyptian guy from the 80s over the current one?