Just out of curiosity, as there are Serbian Orthodox churches in America, say an Irish Catholic converts to Serbian Orthodoxy, are they now Serbian?
They are "a Serb", yes.
Here in CA, there was a guy who was half-Albanian & half-Croat by blood, and he was originally Catholic by religion. He had converted to Serbian Orthodoxy during WWII and joined Mihailovich's forces. He was born and raised in Dubrovnik and came to the US post-war. That guy not only became "a Serb", he was elected the president of the Oakland Serbian Orthodox Church twenty years ago -- and his last name is Albanian.
Likewise for a Scot without a drop of Serb blood who was raised in Scotland and came to the US in his twenties. He married a Serb girl, converted and also became a church president here in CA.
Unfortunately, since the last wars, the wave of Serb refugees who have come to our churches here in the US and find so much seemingly "non-Serb" (translate: "non-Yugoslav")about us, have not liked it. But then again, many of these refugees only learned to cross themselves about fifteen minutes ago, so what do they know?