Judith Rabinowitz obtained legal name change in Bronx County civil court in February 1942
In that Just So story about the Ruby name change, which was speculative, I wondered if Walter Ruby waited until after his father's death in 1917 to go ahead with his plan to shorten his Rabinowiz surname. The elder Joseph was deeply religious and probably proud of his son-of-the-rabbi lineage.
Walter's urge to cement his emerging American identity with an American last name was held in check until Joseph passed away. Walter's older sister Blossom also adopted the Ruby name at that time, though she later took the married name Goldman.
They were the youngest siblings of a family of nine. The oldest was Julius. When he died at age 64 in November 1940, his two surviving children both changed their name to Robbins.
Here we see the February 5, 1942 Bronx county civil court record where Judith Naomi Rabinowitz legally became Judith Naomi Robbins.
I have not yet found a similar record for Abner J. Robbins but I'll keep looking. It seems that Julius was another one who put great respect on the Jewish family name.