A house that is not in harmony with its immediate environment cannot possibly nourish you or create good feng shui energy. So, if you know that the strongest fire feng shui element energy comes to you from the North direction, and not from the South, then of course it is wise to reverse the feng shui bagua.
Here are just a couple basic facts with a simple explanation as to why it is best to reverse the traditional bagua when applying classical feng shui in the Southern hemisphere.
We know that no matter where on earth one is located, the sun always rises in the East and sets in the West. However, in the Southern hemisphere, the Sun moves through the Northern skies to set in the West, while in the Northern hemisphere the Sun's route is through the Southern skies.
Here is more from Wikipedia: "The shadow of a sun dial moves clockwise in the northern hemisphere (opposite of the southern hemisphere). During the day the sun tends to raise to its maximum at a southerly position, whereas in the southern hemisphere it raises to a maximum that is northerly in position (as it tends towards the direction of the equator)".
How can this information help us? In the Southern hemisphere the strongest, most fiery energy of the Sun - the midday Sun - is in the Northern skies, opposite to the strongest Sun energy being in the Southern skies in the Northern hemisphere. It is a reverse, mirror-like expression.
(You can also look into the Coriolis effect; as it all, of course, depends on your point of reference.)
The strongest, Yang/Sun/Fire element energy comes to you from the North, not from the South, as compared to China where feng shui originated from. It is wise - and excellent feng shui - to always respect and listen to your own immediate environment.
There is so much feng shui information out there that uses intimidating notions and Chinese terms that add very little to a successful, practical application of feng shui.
Do you really need to know what Xian Tian or Huo Hai mean? I mean, really. Let's be honest about it - unless you are interested in the historical aspect of feng shui or know Chinese language, this knowledge does very little to help you create an abundance of vibrant, harmonious energy in your home or office.
Trust yourself, listen to the natural rhythms in your surroundings and experiment to discover what truly feels right to you and your home.
Feng shui evolved as a study of one's immediate environment, a study of man's place and connection to universal energies - the land, the sea, the sky, the whole Cosmos. The immediate environment, though, will always come first, because it has the strongest influence on you.
Your environment, the Southern hemisphere environment, obviously has different rhythms as compared to the Northern hemisphere; honour them and adjust any general info accordingly. This especially applies when you practice feng shui, because feng shui is all based on ancient wisdom of honouring nature and nature's rhythms.
Read Part I: Feng Shui Bagua in Both Hemispheres
Continue Reading: How Exactly Do I Apply the Feng Shui Bagua in the Southern Hemisphere?