The last we have concrete evidence because the Old Kingdom and Middle Kingdom Egyptians used maps of their land where the Nile is flowing south . . .
Sorry, but this is not evidence at all. You mix up "south" with the "lower part" of the map, but that is not the same. The Nile always flew from what was called Nubia through Upper Egypt into Lower Egypt and into the Mediterranean Sea. Or from South to North. Physically anything like a reverse flow from the Nile Delta towards Nubia is impossible.
That maps are not always
oriented towards the North however is a fairly common feature. In fact "to orient" originally meant "displaying a map so that the East is ontop", since "
oriens" is Latin for East and in late antiquity and the medieval age maps were "oriented" towards the East (that is Jerusalem).
Maps in antiquity, before the Old World became Christianized, could be oriented towards South and North as well, though. Especially Egyptians liked their maps oriented to the South. That might have been purely for practical reasons, given that most of their civilization lived in the North (Lower Egypt) in later periods (note that the 18th dynasty is neither of the Old nor Middle Kingdom era, but of the New Kingdom era from 1549 BCE onwards) and was thus closer to the viewer, with the more remote Upper Egypt actually ontop. A map facing North will have Upper Egypt on the bottom, and Lower Egypt ontop, and will hence convey an unnatural feeling to the viewer.
In any case, geographical poles are purely conventional and even magnetic poles are to a large extent. What you call North and South is matter of convention, the only "natural thing" about the whole concept is, that the Earth revolves around the Sun and while doing so spins around its own axis. While doing so, the nickel-iron core of the planet builds up a gargantuan magnetic field that has two poles each centering around approximately around one of the geographical poles of the planet, i.e. where the axis of Earth imaginarily lies. Since the planet wobbles quite a bit and revolves not in a circle, but a ellipse, rather than a circle, the magnetic poles are not congruent with the geographical poles.
Thus, not only are the concepts of South and North linguistic conventions and arbitrary to a huge degree, Earth actually has two sets of poles; magnetic and geographic. All this did not matter however to the Egyptians as they new nothing about magnetism and as such cared only for the Sun, stars and in their case the Nile to "orient" themselves. To them geographical orientation was to a huge deal a question of "on which side of the Nile" something was, East equaled morning, life and various important civilizations, West equaled evening, death and the great desert. South was only important as a measurement of "where in Egypt" something was, since the river is to a large part oriented on the North-South axis. North and South became more important when it came to (maritime) navigation, and even then the immediate neighbours lay to the East (Asia) and West (Africa)
Switching poles today would thus only "happen" magnetically. Sure, we would have to reorient all our magnetic tools, practically inverting them. But the concepts of North and South would remain the same. As would all maps, navigational software and denominations.
