I assume the mod was just to make the loco look modern, and had zero aerodynamic advantages.
@OldEastRR , If I am not mistaken, it happened near the end of the streamlining craze, and was one of a kind.
According to Wikipedia:
"No. 1188
K4s #1188 was given a boiler-top streamlined "skyline" casing, but no other streamlining, and was nicknamed "The Skyline". The bell was preserved as well."