daf bit: Chullin 18

The g'mara discusses a time when R. Zera went from his home to Eretz Yisrael and ate food that was considered kosher there but not by his home community. The g'mara argues that when one arrives in a town he must accept the restrictions of the place he has entered and those of the place he has left. The discussion then clarifies: this is true only when going from town to town in Babylon or from town to town in Eretz Yisrael, or when going from Israel to Babylon, but it does not apply when going from Babylon to Israel. R. Ashi says even in this last case if the person intends to return (which R. Zera did not).

I am guessing, but do not know, that the halacha today is not like this. Once you have a tradition (which you probably got from your family) I think you pretty much have it forever, right?