"For choral groups, the Mall prefers no clearly recognizable Christian music, such as carols sung in English, spirituals or gospel."
So you can sneak in a "Stille Nacht" or a "Feliz Navidad" just so long as it's not in English? Might we even be so brave as to sing Adeste Fideles just so long as no one screws up and sings an English verse?
They could play my personal favorites, some Polskie Koledy (Polish Christmas Carols).