The bottom line is that there are a few Chassidim in Australia who avoided crossing the international dateline (IINM instructed to do so by the Rebbe).
I am unaware of any written הוראה, but you can definitely ask the Australian Groners (and IINM also the Serebrianskys, and possibly others).
@dirah Are you aware of any horaa to avoid ever crossing the dateline?
Yes, Reb Arel z”l has such a horaah that he kept meticulously. There may have been others, I don’t know. But was certainly not a הוראה לרבים.
I have also seen a Ksav Yad where the Rebbe advises the Dateline not to be crossed, not sefirah but some other part of the year, I don’t know the context.
Yeshiva shluchim to Australia also always flew with a stop in EY (and IINM also stops in the UK or Europe) on the way.
That began with the third Kvutzah who departed during Sefirah. So you could bring a proof to the contrary from the first two Kevutzos.