I think, in Australia, with the immigrants who would normally interchange their forenames, it would take a generation or three before the practice ceased. I know I have seen the switcheroo going on with the grandchildren of the original immigrant -- and that includes with the Irish immigrants, who also used Saint names, and (if Roman Catholic) also added Confirmation names (also, usually, that of a Saint). Any one of these multiple forenames could, at any time, be the commonly used day-to-day name.
Then, too, because it's Australia, the day-to-day use-name might be none of the above, and, instead, be a nickname as given by workmates, or friends (or even non-friends). Thusly, a person named by their parents/religious reasons as Patrick James Thomas Monahan O'Flaherty might be known as Pat, Paddy, Jimmy, Jim, Tommy, Thommo, Mono, Mondy, "Nathan", "Carrots", or "Blue" (usually for redheads), Chokka, "Jumbo", "Titch", or any number of other appellations.