A shame.
Laws either bind everybody or nobody, there is no "grey" zone inbetween. So, a warrant is out for the guy? Detain him.
Need him as "our war criminal" for ruling the world? Say so.
Just do not, never, celebrate something whatever as UN general secretary with a guy who your own organisation has a warrant out for, you are damaging the institution yyou represent for a huzge salary paid to you (can the institutionbe damaged still, and further?).
FWIW,
Rattler