Together with his great cousin , the Viennese painter Georg Chaimowicz , Rosen came out against the demolition of the Baden synagogue in the late 1980s and prevented the dissolution of the Jewish community in Baden near Vienna.
In 1998 he was elected President of the Baden Jewish Community. Together with the President of the Israelite Cultural Community in Vienna , Ariel Muzicant , Rosen achieved the restoration of the Baden synagogue from public funds in 2002. In the same year, the Center for Intercultural Encounters in Baden , which he is now managing director, was founded. Rosen has been a member of the board of the Jewish Community of Vienna since 2002 and a member of the board of the Federal Association of Jewish Community of Austria. In 2003 he appeared at the Constitutional Convention as spokesman for the Jewish communities in Austria.
In 2004, Federal Minister Maria Rauch-Kallat appointed Rosen Chairman of Senate II of the Equal Treatment Commission, which is now part of the Austrian Federal Chancellery. In this function he was responsible for the treatment of alleged discrimination based on ethnic origin, religion, age and sexual orientation in the world of work and held this office until 2016. In 2008, Rosen was appointed as a judge at the newly established Asylum Court by From 2014 to 2017 he acted as a judge at the Federal Administrative Court in Vienna. He has been working as a freelance consultant since 2017.
In 2007, the Lower Austrian provincial government thanked and recognized him for his commitment to understanding and tolerance. On the occasion of the 70th anniversary of the November pogroms in 1938 , Rosen was awarded the city’s silver coat of arms by the city of Baden .
On November 29, 2012, Rosen was elected Vice-President of the Federal Association of Jewish Religious Communities in Austria and finally entrusted on March 20, 2016 by the Vienna Jewish Community as chargé d’affaires with the management of the Jewish community of Graz for the federal states of Styria, Carinthia and southern Burgenland, which he now also presides over as President. In October he was also appointed to the board of directors of the Jewish Cultural Foundation for Styria, Carinthia and Southern Burgenland. The reestablishment of the Styrian state rabbinate, which was dissolved in 1938, and the appointment of the Viennese rabbi Schlomo Hofmeister are also due to his influence and sustained commitmentto be traced back to the Styrian regional rabbi and chief rabbi of Graz. Rosen’s work for the Jewish community in Graz is clearly marked by an expansion of religious activities and, in a short time, stabilized the Jewish community, which was almost in the process of dissolution. His term of office is also characterized by an increased, representative presence of the Jewish community in public life in the Styrian capital and a clear opening to the outside world. 
Rosen’s work for the Jewish Community of Graz in the educational and cultural field is also characterized by sustainability and diversity. It is also due to his persistent interventions and efforts that the remains of the photographer Dora Kallmus, who became known under the stage name Madame d’Ora , were exhumed on October 24, 2019 in Frohnleiten, Styria, and transferred to the Jewish cemetery in Graz , where she was were buried again on the same day in a grave of honor. 
In public, Rosen consistently stands up for the interests of the State of Israel and against the anti-Israel BDS movement. It is mainly due to his instigation that the state capital Graz and the state of Styria passed resolutions against anti-Semitism and the “anti-Semitic BDS movement” in 2019 and 2020 respectively. There were repeated media disputes, for example with the international law expert Wolfgang Benedek from Graz .