i'm sorry, i don't understand what the question is, nor what the difficulty is …
can you spell it out, please?
Okay, your own words, my bolding:
if we regard something as moving north at speed v faster than light, then an observer moving at speed slower than light but faster than c2/v will regard the same thing as moving south at a speed faster than light …
Problem: I’m aware of Relativity of Simultaneity, but I have never heard of "Relativity of Direction".
Question: If "something" is moving north, let’s say from the South Pole to the North Pole, and another observer is experiencing this "something" as if moving south, i.e. from the North Pole to the South Pole. Where will this "something" finally end up, the South Pole or the North Pole?
Or to keep it simple: One object can’t be in two places at once.