Heh I made that map. Anyhow I feel like contributing more to this thread than a simply "I'm cool" statement.
As has been pointed out already, there was no unified Occitan identity as people considered themselves part of a certain region, such as Gascons, Provençals or whatever. With a 1872 PoD we could have one or more prolific southern French writers or politicians hit his head with a wall and start defending an identity of a common southern French identity based on Occitan language. For this to happen, Occitan would have to be grammarised and standarised, possibly based on the Toulouse dialect. IOTL other languages such as Catalan weren't grammarised until the 1910's and have achieved a certain degree of identitarian unity in the "Catalan Countries" (even if most people outside Catalonia itself are against it). Then we would have the French government not to crack so hard on Occitan and other regional languages as IOTL. Maybe a series of local schools in the south which teach children how to speak French and at least some notions of that centralised Occitan I've already mentioned. This will slow down the rapid decline of Occitan in favour of French and we could add butterflies so more pro-Occitan writers or politicians appear. Of course this is not enough for an independent Occitania or Brittany, but we haven't reached foreign politics yet.
For France to eventually lose land to the United Kingdom and Germany France would have to lose a war against both, preferably at the same time. I'll butterfly the Spanish-American War so it happens early and the Americans manage to pull off a victory, so Spain looks for territorial expansion but it's still outside any of the European Alliances. For an Anglo-French war, we can have the Fashoda Incident blow up into a full-scale war between the two, likely by politicians being stupid. Germany and Italy (and maybe Spain) eventually side with the British to fight off a possible Franco-Russian alliance. Those "Central Powers" win WW1 and impose a peace treaty to France.
Let's assume the treaty confirms German control of Alsace-Lorraine and they somehow don't annex any territory, Italy gains some of it's claimed territories (I can't see them winning all three at the same time). The UK annexes Calais as an occupation zone and some sort of Gibraltar on the Channel, so they can control who enters the Channel. France is left weakened and demilitarised, with governments formed by loose coalitions and radical ideologies slowly creeping on powers. Let's assume communists win, either by a civil war, elections or whatever. That communist government has two ways to go: One would be for it to crack hard on minorities, forcing nationalists to side with the right and foreign powers and for these to succeed; or two, for France to be federal (which would fit better with the "Federal Republic of France" shown in the map) with some sort of Breton or Occitan SSR.
France is ready for round 2 on the 1930's. Somehow the French manage to either defeat or inflict enough damage to Germany so they can safely switch troops to Italy and Spain (for the sake of Occitan independence, these two have fascist* governments, will be explained later). France is eventually crippled and defeated, and partititioned in four major occupation zones (British, German, Spanish and Italian). The Italian and Spanish zones together roughly correspond to Occitania. Britain and Germany agree to an independent Breton state at the end of the war. Belgium is awarded with Pas-de-Calais. Spain wins Basque and Catalan areas, while Italy secures Savoy, Nice and Corsica. Now there' a break within the alliance between the Spanish-Italian fascist* block and an Anglo-German block. The fascists* refuse to unify their part of France with the north and create a separate Occitan republic, basing themselves on Occitan nationalists and a desire to destroy French identity in the area so no pro-French groups emerge.
That first phase of Occitan independence would be confuse and done by force, with massive propaganda and brainwashing starting from a low age. It eventually succeeds and that "Cold War" either lasts until modern times or Occitania refuses to join back to France after it.
About the Swiss expansion, IOTL they were offered Voralberg at the end of WW1 but refused, maybe they could be offered Belfort in the same way and somehow accept, or gain the territory at the end of WW2 after the French invade Switzerland.
Finally, about Normandy, the UK taking control of it is mostly ASB. The closest scenario would be for that area to have a better treating than the rest of France, maybe by not being so thoroughly destroyed during the war. If the breach in quality of life is significant enough, maybe Normans wouldn't want to be annexed into the rest of France in an incredibly narcissistic move. Have a referendum happens in which the "join the UK" option somehow wins and you have it. Probably the most ASB part of the scenario, but it had to be done.