The whole context of Urin's/Uren's appearance and life in Berlin is fascinating. Born in Russian-Poland, he was a citizen of the Russian Empire and undoubtedly obliged to do military service from a young age. In some places, boys as young as 12 were conscripted into the Imperial Army.
This begs the question when did he arrive in Berlin and under what circumstances. Like many Jews, he may have simply been evading military service, particularly in the despised Russian Imperial Army. Many of my German-Jewish male ancestors left Germany to evade such service.
In Berlin, he most probably assumed a German-sounding name to avoid drawing attention to his Eastern European roots. German Jews were well assimilated by the beginning of the 20th century; but there was most definitely discrimination and prejudice against
Ostjuden (Jews from the East) within the Jewish communities themselves. Although, by the time he died in 1936 that would have been increasingly difficult.
The switch back to Klajman is equally intriguing. The Nazis started to implement the anti-Semitic Nuremberg Race Laws soon after gaining power in 1933. However, the key law defining Jews in racial terms was enacted on 14 Nov. 1935; a month after the name change and less than a year before Urin's/Uren's death. Although not exclusively a Jewish surname, there were 30 Jewish Kleinmann families in Berlin in 1931. Maybe Aron/Uren/Urin felt that a change to Klajman would mask his Jewish roots.
Aron's name change was recorded on Benjamin's birth certificate because it directly affected him. As a minor, his surname automatically became Klajman.
Incidentally, Minna Henseleit, who registered Benjamin's birth, was Emma's sister. She was born in Berlin in 1897
https://www.ancestry.co.uk/imageviewer/collections/5753/images/42377_prep808_000282-00393?treeid=&personid=&rc=&usePUB=true&_phsrc=Lpu122&_phstart=successSource&pId=3250041
