About the “j” vs “y” thing: My Hebrew name begins with a Yud. I have German relatives, who though they pronounce my name correctly (with a Yud sound) nevertheless spell it with a J. This is because the “j” in German makes the same sound as a Yud in Hebrew. Thus Joseph is pronounced the same as Yosef. Jacob is pronounced as Yakob (which is the Sephardic pronounciation of Yaacov). Therefore rabbiofberlin (assuming berlin is as in the city in germany) is correct in transliterating a Yud with a “j”.
This does not explain why he would change the spelling of someone’s handle.