If he made the decision to represent France, I doubt he would need to change much from what he is doing at the moment (ie training/competing in his home-town during the Aussie spring/summer with a trip to Europe to compete indoors in February, then going over to Europe around June for as long a season as he wants).

There are plenty of Europeans who fly to countries like South Africa and Australia during their winter for 'warm-weather training' (and sometimes competition). And of course Australia is well suited, time-zone wise, for Tokyo 2020 final preparations.